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Examining the pedagogical content knowledge and practice of experienced secondary biology teachers for teaching diffusion and osmosis

Dissertation
Author: Deanna Lankford
Abstract:
Teachers are the most important factor in student learning (National Research Council, 1996); yet little is known about the specialized knowledge held by experienced teachers. The purpose of this study was twofold: first, to make explicit the pedagogical content knowledge (PCK) for teaching diffusion and osmosis held by experienced biology teachers and, second, to reveal how topic-specific PCK informs teacher practice. The Magnusson et al. (1999) PCK model served as the theoretical framework for the study. The overarching research question was: When teaching lessons on osmosis and diffusion, how do experienced biology teachers draw upon their topic-specific pedagogical content knowledge? Data sources included observations of two consecutive lessons, three semi-structured interviews, lesson plans, and student handouts. Data analysis indicated five of the six teachers held a constructivist orientation to science teaching and engaged students in explorations of diffusion and osmosis prior to introducing the concepts to students. Explanations for diffusion and osmosis were based upon students' observations and experiences during explorations. All six teachers used representations at the molecular, cellular, and plant organ levels to serve as foci for explorations of diffusion and osmosis. Three potential learning difficulties identified by the teachers included: (a) understanding vocabulary terms, (b) predicting the direction of osmosis, and (c) identifying random molecular motion as the driving force for diffusion and osmosis. Participants used student predictions as formative assessments to reveal misconceptions before instruction and evaluate conceptual understanding during instruction. This study includes implications for teacher preparation, research, and policy.

TABLE OF CONTENTS

ACKNOWLEDGEMENTS……………………………………………………………….ii

LIST OF TABLES…..…………………………………………………………………..xvi

LIST OF FIGURES………………………………………………………...………….xviii

ABSTRACT……………………………………………………………………………..xx CHAPTER ONE: INTRODUCTION…………………………………………………….1 Rationale for the Study……………………………………………………………………6 Research Questions………………………………………………………………………10

Sub- Research Questions………...……………………………………… ……….10 Theoretical Framework…………………………………………………………………..11 Knowledge for Teaching Held by Experienced Teachers……………………….12 Models of Teacher Knowledge…………………………………………………..13 Orientations to Science Teaching………………………………………………..23

Constructivist Orientation to Science Teaching…………………………………23

Knowledge - transmission Orientation to Science Teaching……………………...24 Taxonomy of PCK……………………………………………………………….24 5E Instructional Model…………………………………………………………..27

Engagement ………..…………………………………………………….28

Exploration………………………………..……………………………...28

Explanat ion…………..…………………………………………………..28

Elaboration………………………..……………………….……………..29

Evaluation…………..……………………………………………………29

Content Representation (CoRe)……………………..…………………………...30

v Diffusion and Osmosis…………………………………………………………30 Significance of the Study……………………………………………………………….33 Organization of the Dissertation………………………………………………………..35 CHAPTER TWO: REVIEW OF LITERATURE………………………………………37 The Nature of PCK…………………………………………………………………..…38 Teacher Knowledge Held by Prospective Teacher s of Mathematics and Science……..39

Prospective Mathematics Teachers……………………………………………..39

Prospective Science Teachers…………………………………………………..41 Knowledge for Teaching Held by Experienced Teachers...............................................47

Experienced Mathematics Teachers…………………………………………...47

Experienced Science Teachers………………………….………………………51

Orientation to Science Teaching………………………………………..53

Knowledge of Representations…………………………………………57

Knowledge of Instructional Strategies………………………………….59

Knowledge of Students’ Understanding of Science……………………63

Knowledge of Assessment………………………………………….…..67

Knowledge of Science Curriculum…………………………….….……72

Knowledge Integration…………………………………………….……75

Topic - specific PCK for Teaching Diffusion and Osmos is……………………...78 Review of Practitioner Literature for Teaching Osmosis and Diffusion………..78 Review of Science Education Research Literature Examining Teaching and

Learning Related to Diffu sion and Osmosis……………………………………80

Gaps within the Literature………………………………………………………………84 CHAPTER THREE: THE RESEARCH PROCESS……………………………………88

vi

Research Questions and Tradition………………………………………………………88

Constructivism…………………………………………………………………..89

Epistemological Assumptions…………………………………………………..91

Ontological Assumptions……………………………………………………….93 Context of the Study…………………………………………………………………….94

Overview of ASTEP…………………………………………………………….94

Selection of Mentor Teachers……………………………………………95

ASTEP Research Project………………………………………………………...95

My Role in ASTEP - RP…………………………………………………..97 Study Participants………………………………………………………………………..98

Purposeful Sampling……………………………………………………………..98

Participant Schools/Districts……………………………………………………..99 Design of the Study……………………………………………………………………..103

Case Study Approach…………………………………………………………...103

Methodological Assumptions…………………………………………..106

Limitations of Case Study Research……………………………………106 Role of the Researcher………………………………………………………………….108

Institutional Review Board……………………………………………………..110

Data Collection…………………………………………………………111

Les son Plans…………………………………………………………….112

Pre - observation Interview………………………………………………113

Field Observations……………………...………………………………113 Stimulated Recall Interview……………………………………………114

vii

Data Analysis……………………………………………………………………...……115

Development of Codes………………………………………………………….115

Case Profile.……..……………………………………………………………...116

Cross - case Comparison…………………………………………………………117 Trustworthiness…………………………………………………………………………117

Triangulation……………………………………………………………………118

Member Checking………………………………………………………………119

Pee r Debriefing…………………………………………………………………119 CHAPTER FOUR: CASE PROFILES…………………………………………………121 Emma’s Case Profile……………………………………………………………………122 Emma’s Vignette: Make a Prediction…………………………………………………..122

Background and Context……………………………………….…….…………125

Orient ation to Science Teaching……………………………….….……………126

Goals and Purposes of Instruction………………………….…………..126

Perception of Teacher Role…………………………………….….……128

Perception of Student Role………………………………………….….129

Ideal Images of Teaching……………………………………………….130

View of Science as a Discipline………………………………………...131

Summary of Emma’s Orientation to Science Teaching………………...133

Lesson Plan………………………………………………………………….….134

Knowledge of Representations and Instructional Strategies..…….……………137

Knowledge of Student s’ Understanding of Science……………………………142

Knowledge of Assessment……………………………………………………...146

viii

Knowledge of Curriculum…………………………………………………….149

Emma’s PCK for Teaching Diffusion and Osmosis…………………………..150

Content Representation………………………………………………………..154 Ca thy’s Case Profile…………………………………………………………………...158 Cathy’s Vignette: The Power of a Story……………………………………………….158

Background and Context……………………………………………………….160

Orientation to Science Teaching………………………………………………..161

Goals and Purposes for Instruction……………………………………..161

Perception of Teacher Role……………………………………………..163

Perception of Student Role……………………………………………..166

Ideal Images of Teachi ng……………………………………………….166

View of Science as a Discipline……………………………..…………168

Summary of Cathy’s Orientation to Science Teaching…………………169

Lesson Plan……………………………………………………………………..170

Knowledge of Representations and Instructional Strategies…………………...174

Knowledge of Students’ Understanding of Science……………………………179

Knowledge of Assessment……………………………………………………...184

Knowledge of Curriculum………………………………………………...……187

Cathy’s PCK for Teaching Diffusion and Osmosis……………………….……189

Content Representation…………………………………………………………194 Janis’ Case Profile………………………………………………………………………197 Janis’ Vignette: Effective Analogies…………… …………………………………...…197

Background and Context…………………………………………….…………201

ix

Orientation to Science Teaching………………………………………………201

Goals and Purposes of Instruction……………………………………..201

Perception of Teacher Role…………………………………………….203

Perception of Student Rol e……………………………………………..207

Ideal Images of Teaching……………………………………………….207

View of Science as a Discipline………………………………………..208

Summary of Janis’ Orientation to Science Teaching…………………..209

Lesson Plan……………………………………………………………………..211

Knowledge of Represe ntations and Instructional Strategies…………………...213

Knowledge of Students’ Understanding of Science……………………………217

Knowledge of Assessment……………………………………………………..221

Knowledge of Curriculum………….…………………………………………..224

Janis’ PCK for Teaching Diffusion and Os mosis………………………………226

Content Representation…………………………………………………………231 Jason’s Case Profile…………………………………………………………………….235 Jason’s Vignette: Talk Like a Scientist…………………………………………………235

Background and Context……………………………………………………….239

Orientation to Science Teaching……………………………………………….240

Goals and Purposes of Instruction……………………………………..241

Perception of Teacher Role…………………………………………….243

Perception of Student Role…………………………………………….244

Ideal Images of Teaching………………………………………………245

View of Science as a Discipline………………………………………..247

x

Summary of Jason’s Orientation to Science Teaching………………248

Lesson Plan…………………………………………………………………..250

Knowledge of Representations and Instructional Strategies…………………253

Knowledge of Students’ Understanding of Science………………………….257

Knowledge of Assessment……………………………………………………259

Knowledge of Curriculum…………………………………………………….262

Jason’s PCK for Teaching Diffusion and Osmosis……………………………265

Content Representation………………………………………………………..268 Kacy’s Case Profile……………………………………………………………………272 Kacy’s Vignette: Making and Testing Predictions…………………………………….272

Background and Context……………………………………………………….276

Orientation to Science Teaching……………………………………………….277

Goals and Purposes of Instruction……………………………………..277

Perception of T eacher Role…………………………………………….280

Perception of Student Role…………………………………………….283

Ideal Images of Teaching………………………………………………284

View of Science as a Discipline………………………………………..285

Summary of Kacy’s Orientation to Science Teaching…………………286

Lesson P lan…………….……………………………………………………….287

Knowledge of Representations and Instructional Strategies…….…………..…290

Knowledge of Students’ Understanding of Science…………….…………...…294

Knowledge of Assessment……………………………………….…………….296

Knowledge of Curriculum………………………………………..……………298

xi

Kacy’s PCK for Teaching Diffusion and Osmosis……………………………300

Content Representation………………………………………………………..303 Lana’s Case Prof ile……………………………………………………………………305 Lana’s Vignette: Investigating Osmosis and Diffusion with Baggies…………………305

Ba ckground and Context……………………………………………………….309

Orientation to Science Teaching………………………………………………..309

Goals and Purposes of

Instruction……………………………………...310

Perception of T eacher Role…………………………………………….313

Perception of Student Role……………………………………………..315

Ideal Images o f Teaching……………………………………………….316

View of Science as a Discipline………………………………………..319

Summary of Lana’s Orientatio n to Science Teaching………………….320

Lesson Pla n……………………………………………………………………..322

Knowledge of Representations and Instructi onal Strategies…………...………324

Knowledge of Students’ Unders tanding of Science……………………………329

Knowledge of Ass essment………………………………………….………….331

Knowledge of Curr iculum………………………………….…………………..333

Lana’s PCK for Teaching Diffu sion and Osmosis……………………………..336

Content Represe ntation…………………………………………………………340 CHAPTER FIVE: CROSS - C ASE ANALYSIS………………………………………..343 Sub- research Questions...……………………………………………………………….343 Assertions……………………………………………………………………………….344

xii

Assertion 1: The majority of the participants held co nstructivist orientations

to teaching science. Reflection on their high school biology teaching experience

and extensive knowledge of their students and specific school context were the primary sources of their science teaching orientations………………………………344

Overview of Orientations for Teaching Biology……………………………..344

Nature of Teachers’ Orientation t o Science Teaching………………………..345

Dimensions of Teacher Orientation…………………………………………..346

Overview………………………………………………………………346

Goals and Purposes for Teac hing Science……………………….…….346

Perception of Teac her Role…………………………………….….…...347

Perception of St udent Role…………………………………….….……348

View of Science as a Discipline……………………………….…..……348

Sources of Teacher Orientation to Science Teaching……….………………….350

Teaching Expe rience………………………………….………………...350

Professional Lear ning Teams………………………….………………..351

Partnership for Research and Ed ucation with Plants….………………..351

Summary………………………………………………………………………..352 Assertion 2: The teachers used representations at the molecular, cellular, and plant

organ levels which served as the foci for demonstrations, analogies, and student

investigations. The majority of the teachers sequenced their instruction to have students explore the phenomena of diffusion and osmosis pr ior to constructing explanations through teacher - led intera ctive lectures…………………..………………353

Diffusion …………………………………………………………..……………355

Representations at the Cellul ar Level………………….…………..…………...356

Plant Cells within Elodea

Leaves………………….………….….……357

Decalcified Chi cken Eggs………………………………….……….….357

Artificial Cel l Models…………………………………………….….…359

xiii

Virtual Cel l Models…………………………………………………….360

Representations of osmosis in Plant Organs………………………….………..362

Lettuce Leaves………………………………………………….………3 62

Potato Slic es……………………………………………….…….……...362

Interactive Lect ures……………………………………………………….…….364

Interactive Lectu re Format……………………………………….….….364

Instructional Se quence………………………………………………………….364

Exploration of Phenomena……………………………………………...365

Exp lana tion……………………………………………………………..366

Elaboration……………………………………………………………...367

Practical Applica tions…………………………………………………………..368

Summary ………………………………………………………………….…….368 Assertion 3: The teachers identified three major areas of potential learning difficu lties

Associated with students’ conceptual understanding of diffusion and osmosis

(a) comprehension of vocabulary terms (hypertonic, hypotonic, isotonic, concentration)

and students’ ability to use vocabulary appropriately, (b) accurate prediction of the direction of net water movement during osmosis, and (c) difficulty visualizing and

understanding osmosis and diffusion at the molecular level……………………..…….369

Vocabulary as a Potential Learning Di fficulty for Students……………………370

Predicting the Direction

of Osmosis……………………………………………371

Visualizing Random Molecular Motion as the Driving Force for

Diffusion and Osmosis…………………………………………………………372

Summar y……………………………………………………………………….373

Assertion 4: All teachers relied upon students’ predictions to: (a) re veal students’ prior knowledge, (b) assess students’ current conceptual understanding, and (c) inform

instructional decisions whil e teaching…………………………………………………373

Formative Assessme nts………………………………………………………………..373

xiv

Pre - assessment of Diffusion…………………………………………………..375

Pre - assessment o f Osmosis……………………………………………………375

Making and Testing Predictions d uring Instruction…………………………..376

Student Explanations………………………………………………………….377

Teacher Obser vations…………………………………………………………378

Instructional Responses to For m ative Assessments…………………………..378

Computer Animations……………….………………………………..379

Diagr ams…………………………………………………….………..380

Analo gies……………………………………………………………..380

Summary ………………………………………………………….…………..381 Assertion 5:

Teachers relied upon state guidelines to i dentify learning goals related to diffusion and osmosis. They met or exceeded state guidelines by teaching random molecular motion as the driving force for the phenomena and included practical applications. The teachers made explicit connections across the horizontal curriculum ……………………… .……………………………………………………….381

General Biology Curriculum for Teaching Osmosis and Diffusion…………..381

Horizontal Curricular Connections……..……………………………………..382

Summa ry………………………………………………………………………383 Assertion 6: Teachers drew o n their highly integrated PCK to create learning opportunities designed to scaffold students’ learning of osmosis and diffusion, progressing from concrete to abstract representations ………………………….……..383

Lesson Progression from Concrete to Abstract Represe ntations…………...….386

Student Predictions as a Form ative Assessment…………………………….…387

Summar y………………………………………………………………….……388 CHAPTER SIX: CONCLUSIONS

AND IMPLICATIONS……….………………….390

Research Questions and Sub - questions…………………………….…………….……390

xv

Summary of Res earch Fi ndings…………………………………………………..……391 Question One: The Nature and Sources of Teachers’ Orientation

to Teaching Bio logy……………………………………………………….…..391

Question Two: Experienced Biology Teachers’ Knowledge of

Representations and Instructional Strategies for Teaching

Diffusion and Osmosis…………………………………………………………392

Question Three: Knowledge of St udents as Learners………………………….392

Question Four: Knowledge and Utilization of Formative Assessment………..393

Question Five: Teacher Organization and Sequence of the

Biology Curr iculum……………………………………………………………394

Question Six: The Integration of PCK Components ………………………..…395 Discussion……………………………………………………………………………...395 Orientation to Scienc e Teaching………………………….……………………395 Teacher Knowledge of Representations and Instr uctional Strategies………….399 Teacher Knowledge of Students’ Unde rstanding of Science…………………..402 Teacher Knowledge of Assessm ent in Science………………………………...405 Teacher Knowledge of Scienc e Curriculum………………………………..…..407 Knowledge Integration and Topic - specifi c PCK Model………….……………408 Implications………………………………………………………………….…….…...411

For Teacher Preparat ion……………………………………….….………...….411

For Experienced Te achers…………………………………….…….…….……413

For Research ………………………………………………………..…………..415

For Policy…………………………………………………………….…………416 Conclusion…………………………………………………………………….………..418

Orientation to Science Teaching…………………………………………..……418

xvi

Knowledge of Representations and Ins tructional Strategies……………….…419

Knowledge of Students Unders tanding of Science……………………………419

Knowledg e of As sessment……………………………………………….……420

Knowledge of Cur riculum………………………………………………….….421

Knowledge Inte gration…………………………………………………………421 REFERENCE S…………………………………………………………………………423 APPENDIX A… ………………………………………………………………………..454 APPENDIX B…………………………………………………………………………..461 APPENDIX C… ………………………………….…………………………………….463 APPENDIX D… ……………………………………….……………………………….465 APPENDIX E… ………………………………………………………………………..466 VITA……………………………………………………………………………………467

xvii

LIST OF TABLES

Table

1. U.S. fourth and eighth graders pe rformance in science on the 2003 and 2007 TIMSS ………………………………………………………………………..2

2. Timeline of APB teacher certification program ……………………………………94

3. ASTEP - RP data collection points ………………………………………………….96 4. Participants’ Personal Data …………………………………………………………98 5. Comparison of Societal Factors between Participant’s School Districts ………….100 6. Contextual Factors in Participants’ School ………………………………………..100 7. Comparison of Ethnic Diversity …………………………………………………..101 8. Analysis of Graduates in Participants’ School Districts…………………………..102 9. Data Collection Matrix……………………………………………………………114 10. Emma’s lesson plan for Day 1………………………………………….………...135 11. Emma’s lesson plan for Day 2…………………………………………………..136 12. Content r epresentation for Emma ………………………………………………..155 13. Cathy’s lesson plan for Day 1……………………………………………………171 14. Cathy’s lesson plan for Day 2……………………………………………………172 15. Content representation for Cathy …………………………………………………194 16. Janis’ lesson plan fo r Day 1 ………………………………………………………211 17. Janis’ lesson plan for Day 2………………………………………………………212 18. Content representation for Janis …………………………………….…………….231 19. Jason’s lesson plan for Day 1…………………………………………….……….250 20. Jason’s l esson p lan for Day 2 ……….………………………………….…………252 21. Content representation for Jason…………………………………….……………269

xviii

22. Kacy’s l esson p lan for Day 1 ……………..………………………………...….288 23. Kacy’s lesson plan for Day 2…………………………………………………..289 24. Content representation for Kacy……………………………………………….304 25. Lana’s lesson plan for Day 1…………………………………………………..323 26. Lana’s lesson plan for Day 2…………………………………………………..325 27. Content representation for Lana……………………………………………….341 28. Dimensions of teacher’ orientation for science teachi ng ………………………350 29. Representations and instructional strategies implemented by participants …….355 30. Representations of Diffusion………………………………………………...…357

31. Living cells as representations for osmosis …………………………………….358 32. Decalcified chicken eggs as cell and membrane representations ………………359 33. Artificial cell models and semipermeable membrane representations …………360 34. Virtual representations of a red blood cell and IV solution……………………..361 35. Lettuce leaves as representations for osmosis …………………………………..362 36. Potato slices as representations for osmosis ……………………………………..363 37. Sequence of concept introduction during the lesson…………………………….365 38. Implicit 5E instructional sequence………………………………………………367 39. Overview of teacher knowledge of students’ understanding of science …………370 40. Pre - assessment and formative assessments for osmosis and diffusion…………..374 41. Teacher response to pre - assessments and formative assessments ……………….379

xix

LIST OF FIGURES

Figure

1. Grossman (1990) model for pedagogical content knowledge ….…….…………….16 2. Magnusson et al. (1999) model of teacher knowledge ………….……….…………19 3. Magnusson et al. (1999) PCK model …………………………………….…………20 4. Veal and MaKinster (1999) hierar chical model of teacher knowledge ………….…25 5. Sources of Emma’s o rientation to s cience t eaching ………………………………133 6. Diagram of decalcified eggs in distilled water (A) and in corn syrup (B) ……......139

7. Emma’s topic - specific PCK …………………………………………………….…151 8. Integration of Emma’s topic - specific PCK ………………………………………..153 9. Sources of Cathy’s orientation to science teaching ……………………………….169 10. Cathy’s topic - specific PCK ………………………………….…………………….190 11. Integration of Cathy’s topic - specific PCK … …………………………………...…192 12. Sources of Janis’ orientation to science teaching …………………………………210 13. Janis’ topic - specific PCK ………………………………………………………….227 14. Integration of Janis’ topic - specific PCK ……………………………………….….228 15. Sources of Jason’s orientation to science teaching …………………………….….249 16. Whiteboard diagram of dialysis investigation………………………………….…254 17. Jason’s topic - specific PCK ……………………………………………………..…265 18. Integration of Jason’s topic - specific PCK ………………………………………...267 19. Sources of Kacy’ s orientation to science teaching ………………………………..286 20. Representation of osmosis ………………………………………………………...293 21. Kacy’s topic - specific PCK …………………………………….………………….301

xx 22. Integration of Kacy’s topic - specific PCK …………………………………………302 23. Sources of Lana’ s orientation to science teaching …………...……………………321 24. Diagram illustrating direction of osmosis …………………………………………326 25. Lana’s topic - specific PCK ……………...…………………………………………337 26. Integration of Lana’s topic - specific PCK …………………………………………338 27. Integr ation of teacher knowledge for teaching osmosis and diffusion ……………385 28. Model of PCK for teaching diffusion and osmosis ……………………………….410

xxi

EXAMINING THE PEDAGOGICAL CONTENT KNOWLEDGE AND PRACTICE OF EXPERIENCED SECONDARY BIOLOGY TEACHER S FOR TEACHING DIFFUSION AND OSMOSIS

Deanna M. Lankford

Dr. Patricia M. Friedrichsen, Dissertation Supervisor

ABSTRACT

Teachers are the most important factor in student learning (National Research Council, 1996); yet little is known about the specialized knowledge held by experienced teachers. The purpose of this study was twofold: first, to make

explicit

the pedagogical content knowledge (PCK) for teaching diff usion and osmosis held by experienced biol ogy teachers and , sec ond, to reveal how t opic - specific PCK informs teacher practice . The Magnusson et al. (1999) PCK model served as the

theoretical framework for the study. The overarching research question was: When teaching lessons on osmosis and diffus ion, how do experienced biology teachers draw upon their topic - specific pedagogical content knowledge? Data sources included observations of two consecutive lessons, three semi - structured interviews, lesson plans, and student handouts . Data analysis indicated five of the six teachers held a constructivist orientation t o science teaching and engage d students in explorations of diffusion and osmosis prior to i ntroducing the concepts to students. Explanations for diffusion and osmosis were based upon students ’ observations and experiences during explorations. All six teachers used representations at the molecular, cellular , and pl ant organ levels to serve as

foci for

explorations of diffusion and osmosis . Three potential learning difficulties identified by the

teachers included: (a) understanding vocabulary terms , (b) predicting the direction of

xxii

osmosis, and (c) identifying random molecular motion as the driving force for diffus ion and osmosis . Participants used s tudent predictions as formative assessments to r eveal misconceptions before instruction and evaluate conceptual understanding during instruction. This study includes implications for teacher preparation, research, and policy.

1 CHAPTER ONE: INTRODUCTION

Achieving sci entific literacy became a major goal in science education with the launch of Sputnik in 1957 (Bybee, 1997; DeBoer, 2000; Hurd, 1998). In the 1990s, “scientific literacy was the single term expressing the purposes of science education” (Bybee, 1997, p. 64). DeBoer (2000) noted the importance of science education for the general population in the United States in terms of “the public’s attitude toward science and their ability to serve as thoughtful critics of the role of science in society” (p. 584). Thus, a s the world becomes increasingly reliant upon science, mathematics, and technology, there is genuine concern about the quality and effectiveness of science education in the U.S. (American Association for the Advancement of Science, 1993; Bybee, 1997; Hurd, 1998; Phillips, 2007). When students fail to develop a basic understanding of scientific concepts and the processes and methods of science, they perceive science as separate from their lives. This is especially troubling in a world increasingly reliant u pon science and technology; thus, the scientific literacy of the American populace is of great concern. According to the National Science Board (2004), the average citizen in the United States understands very little about science. The United States must s ignificantly increase the scientific and mathematical competency among K - 12 students to ensure an adult population able to understand and reach consensus on policies addressing the world’s most pressing problems (National Science Board [NSB], 2004; Phillips, 2007).

Concerns about the quality and effectiveness of science education in the United States are mounting as American youth fall behind their international peers in other nations in terms of knowledge of science and technology (Bybee, 1997; DeBoer, 1991;

2 DeBoer, 2000; NSB, 2004; Phillips, 2007). There is a significant body of evidence indicating American youth are ranked well below the highest achieving countries (Phillips, 2007; Trends in International Mathematics and Science Study ( TIMSS ), 2003, 2007). International data on students’ knowledge of science collected from Trends in International Mathematics and Science Study (TIMSS) indicates that U.S. eighth - grade students’ performance (see Table 1) was above the international average for both the 2003 and 2007 TIMSS (National Center for Educational Statistics

[NCES] 2003; 2007) ; however, this picture is not as bright as it seems. Table 1 1, 2 . U.S. fourth and eighth graders performance in science on the 2003 and 2007 TIMS S

2003 Results

2007 Results

E ighth grade

Eighth grade

U.S. eighth grade students scored 527, on average, exceeding the international average of 473.

U.S. eighth - graders scored 520, on average, in science, which was higher than the TIMSS scale average of 500.

The average eighth - grade

science scores exceeded eighth - grade science scores in 32 countries, fell below that of 6 countries (Asian and European), and was not measurably different from scores in 5 countries.

The average U.S. eighth - grade science score exceeded that of science sco res in 35 countries, was lower in 9 other countries (Asian and European) and not measurably different from 3 countries.

It is important to note that in 2003, eighth graders in the United States scored above the international average in science achievem ent by an average of 54 points ( NC E S, 2003); while in 2007 eighth graders in the United States were only able to maintain an average lead of 20 points above the international average score for science ( NC E S, 2007). Another concerning statistic is that U.S. eighth graders were out performed by their peers in five other countries in 2003; while in 2007, U.S. eighth

_________________________

1 Note: From “Highlights from the Trends in International Mathematics and Science Study (TIMSS) 2003.” By National center for Educational Statistics (2005). Washington D.C.: Retrieved

on August 10, 2009 from http://nces.ed.gov/pubs2005/timss03/science1.asp

2 Note: From “Highlights from TIMSS 2007: Mathematics and Science Achievement of U.S. Fourth -

and E ighth - Grade Students in an International Context.” By National Center for Educational Statistics. Washington D.C.: Retrieved on August 10, 2009 from http://nces.ed.gov/pubs2005/timss03/scienc e1/asp

3 graders fell below nine other countries ( NC E S, 2003, 2007). Overall, the U.S. performance in science was significantly lower than that of many Asian and European countries including Singapore, Republic of Korea, Hong Kong, Taipei, Japan, Netherlands, Hungary, and the Flemish portion of Belgium . Another significant concern is the low number of U.S. youth preparing for careers in science, technology, engineering, and mathematics (STEM); only 16 percent of all postsecondary degrees in the United States are related to STEM fields and many of these postsecondary degrees are awarded to foreign students (Phillips, 2007). Linda Froschauer , former preside nt of the National Science Teachers Association (NSTA), reported the number of engineering degrees awarded in the United States has decreased by 20 percent from 1985. South Korea, a nation with approximately one - sixth of the U.S. population, graduates as m any engineers as the United States. This is a disturbing trend as 15 of the 20 fastest growing occupations projected for 2014 require significant science and mathematics knowledge ( Froschauer , 2006).

Students develop their attitudes toward science and the ir understanding of science throughout their K - 12 educational experiences. Therefore, teachers are a critical factor in student learning (Committee on Science and Mathematics Teacher Preparation [CSMTP], 2001; King & Newman, 2000). Teachers control the lea rning environment and ultimately determine what is taught, when it is taught, and how it is taught (Abell, 2007; CSMTP, 2001; King & Newman, 2000). To be successful, teachers must have strong subject matter knowledge, understand the nature of science, be a ble to translate scientific concepts into meaningful learning experiences for their students, and highlight

4 applications for science within society and in the lives of students (Gess - Newsome, 1999). The National Science Education Standards (NRC, 1996) de scribes effective science learning as occurring when learners are actively engaged in science; making connections between scientific concepts; applying their knowledge of science to problem solving; supporting claims with evidence; and reflecting upon thei r methods, processes, and conclusions. This description of science learning requires that science teachers have a deep and flexible understanding of science subject matter and scientific concepts, as well as an understanding of students as learners, knowle dge of instructional strategies, representations, assessment strategies, and curricular resources (Darling - Hammond, 2008). Schwab (1971) described teacher knowledge in practical terms as the wisdom of practice developed through classroom experience. Feima n- Nemser (2001) notes that knowledge for teaching develops with experience as teachers learn to blend their knowledge of students as learners with their knowledge of content to make concepts understandable. Verloop, Van Driel, and Meijers (2001) posit teac her knowledge is closely related to individual experiences and contexts and, therefore, unique to the individual. Successful teachers are able to transform their knowledge of scientific concepts into a form of knowledge that can be understood by learners b y integrating their knowledge of learners, representations, instructional strategies, assessments, and curricular resources to create meaningful learning opportunities that make connections between lesson content and students’ experiences (Shulman, 1987). To be effective, teachers need to (a) activate prior knowledge,

(b) predict student difficulty with content,

5 (c) adjust teaching approaches and strategies to better address diverse student

learning needs, (e) ma ke connections between concepts, (f) identify relevant connections be tween content and student lives, (g) provide opportunitie s for students to assess their learning, (h) use feedback on formative assessments to inform instruction, and (i) align instructional goals and methods with the topics being t aught (Barnett & Hodson, 2001; Doyle, 1985; Lee, Brown, Luft, & Roehrig, 2007; Lee & Luft, 2006; Magnusson et al.

1999; Treagust, 1987; van Driel, Verloop, & de Vos, 1998). Shulman (1987) identified pedagogical content knowledge (PCK) as a unique form of knowledge expressly for teaching. He described PCK as including subject matter knowledge, knowledge of potential student learning difficulties and students’ prior knowledge for specific concepts, as well as the most effective models, analogies, illustratio ns, explanations, and investigations to make the concept understandable for students. “In a word, the ways

of representing and formulating the subject that make it comprehensible to others ” (Shulman, 1986, p. 9).

Grossman (1990) expanded upon Shulman’s (1986) ideas to emphasize four general areas of teacher knowledge including: subject matter knowledge; general pedagogical knowledge; knowledge of context; and the core of Grossman’s model, pedagogical content knowledge (PCK). Grossman (1990) defined PCK as consisting of four components: (1) knowledge and beliefs about the purposes and goals for teaching science, (2) knowledge of students’ understanding of science, (3) knowledge of science curricula and curricular resources, and (4) knowledge of representatio ns and instructional strategies.

6 Magnusson, Krajcik, and Borko (1999) build upon the work of Grossman (1990) to conceptualize pedagogical content knowledge (PCK) as consisting of five components: (1) teacher orientation for science teaching, ( 2) knowledge of students understanding of science, (3) knowledge of representations and instructional strategies, (4) knowledge of assessment, and (5) knowledge of curriculum (p. 96). Topic - specific PCK is described by Magnusson et al. (1999) as the knowle dge representations and instructional strategies useful for teaching a specific topic in science, the knowledge of potential student learning difficulties and prior knowledge associated with the topic, knowledge of the most effective assessment strategies to reveal students’ understanding of the topic, as well as knowledge of the science curriculum and curricular resources. Thus, PCK necessary for teaching specific topics in science would be unique to that topic. Abell (2008) conceptualizes PCK to include four important characteristics: (1) PCK includes discrete categories of knowledge applied synergistically during teaching, (2) PCK is dynamic and continually changing as teachers gain teaching experience, (3) knowledge of subject matter is central to PCK, and (4) PCK supports the transformation of subject matter knowledge into a form of knowledge understandable for students. PCK is not only about knowledge the teacher possesses it is also highly reflective of the quality of teacher knowledge, teaching exper ience, and the manner in which the components of PCK are integrated to create effective learning experiences (Abell, 2008).

Rationale for the Study

Reform - minded science teachers actively engage students in a way that prepares students

to :

apply scientifi c principles and processes to decision making; understand the natural world; and consider careers in science, technology, engineering, or mathematics

7 (NRC, 1996; Texley & Wild, 2004). In her chapter on science teacher knowledge, Abell (2006) noted that “un derstanding the development of teacher subject matter knowledge and PCK is critical for our success in science teacher education” (p. 1133). Historically, it has been the role of science teacher educators to provide insight into the what, why, and how of t eaching for prospective and novice teachers (DeBoer, 2000). In order to understand the knowledge needed for teaching, it is important to investigate the nature of PCK held by experienced teachers and how that knowledge informs their teaching.

What is lar gely missing from the literature is research into the knowledge and beliefs held by experienced teachers and how their beliefs about teaching and learning, and their knowledge of learners, instructional strategies and representations, curriculum, and asses sment are drawn upon during teaching and reflecting. Examining experienced teachers’ knowledge for teaching can inform the design of teacher education programs. A deeper understanding of the knowledge experienced teachers draw upon when teaching and planni ng provides important insight for science teacher educators as they define goals and design programs and coursework for prospective teachers (Abell, 2008). Learning to teach does not mean learning to survive within the classroom; it means learning to syst ematically organize knowledge so that it can be drawn upon and applied to new situations (Berliner, 2001). Unfortunately, experienced teacher knowledge is not well documented. Loughran, Berry and Mulhall (2006) noted: “A real and serious issue in teaching is the ability to capture, portray and share knowledge of practice in ways that are articulable and meaningful to others” (p. 15).

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Abstract: Teachers are the most important factor in student learning (National Research Council, 1996); yet little is known about the specialized knowledge held by experienced teachers. The purpose of this study was twofold: first, to make explicit the pedagogical content knowledge (PCK) for teaching diffusion and osmosis held by experienced biology teachers and, second, to reveal how topic-specific PCK informs teacher practice. The Magnusson et al. (1999) PCK model served as the theoretical framework for the study. The overarching research question was: When teaching lessons on osmosis and diffusion, how do experienced biology teachers draw upon their topic-specific pedagogical content knowledge? Data sources included observations of two consecutive lessons, three semi-structured interviews, lesson plans, and student handouts. Data analysis indicated five of the six teachers held a constructivist orientation to science teaching and engaged students in explorations of diffusion and osmosis prior to introducing the concepts to students. Explanations for diffusion and osmosis were based upon students' observations and experiences during explorations. All six teachers used representations at the molecular, cellular, and plant organ levels to serve as foci for explorations of diffusion and osmosis. Three potential learning difficulties identified by the teachers included: (a) understanding vocabulary terms, (b) predicting the direction of osmosis, and (c) identifying random molecular motion as the driving force for diffusion and osmosis. Participants used student predictions as formative assessments to reveal misconceptions before instruction and evaluate conceptual understanding during instruction. This study includes implications for teacher preparation, research, and policy.