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Developing Mathematical Reasoning
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Developing Mathematical Reasoning
The Strategies, Models, and Lessons to Teach the Big Ideas in Grades 3-5



March 2026 | 344 pages | Corwin

Math is not rote-memorizable. Math is not random-guessable. Math is figure-out-able.

Author Pamela Weber Harris argues that teaching real math—math that is free of distortions—will reach more students more effectively and result in deeper understanding and longer retention. This book is about teaching undistorted math using the kinds of mental reasoning that mathematicians do.

Memorization tricks and algorithms meant to make math “easier” are full of traps that sacrifice long-term student growth for short-lived gains. Students and teachers alike have been led to believe that they’ve learned more and more math as they move through the content, but in reality students are not necessarily progressing in their ability to reason mathematically.

Using tricks may make facts easier to memorize in isolation, but that very disconnect distorts the reality of math. The mountain of trivia piles up until students hit a breaking point. Humanity's most powerful system of understanding, organizing, and making an impact on the world becomes a soul-draining exercise in confusion, chaos, and lost opportunities.

In her landmark book Developing Mathematical Reasoning: Avoiding the Trap of Algorithms, Pam emphasized the importance of teaching students increasingly sophisticated mathematical reasoning and understanding underlying concepts rather than relying on set rules for solving problems. Now, this next companion volume, Developing Mathematical Reasoning: The Strategies, Models, and Lessons to Teach the Big Ideas in Grades 3–5, equips educators with practical tools to move beyond rote memorization toward true mathematical thinking for students in upper elementary grades. Focusing on additive and multiplicative reasoning, the book introduces strategies designed to improve mathematical reasoning, Problem Strings, and strategic modeling to strengthen student understanding.

Highlights include:

  • Reasoning-based strategies: Replace traditional algorithms with approaches that build critical thinking while ensuring understanding
  • Problem Strings: Step-by-step guidance on walking students through a sequence of problems that spark insight
  • Grade 3–5 focus: Comprehensive coverage of additive and multiplicative reasoning tailored for upper elementary learners
  • Practical tools: Ready-to-use routines, discussion prompts, and modeling techniques for immediate classroom application

Help students learn to think mathematically rather than memorize. Build confidence, deep understanding, and an appreciation for the logic and beauty of math.

 
Preface
About This Book

 
Language Use in This Book

 
 
Acknowledgments
 
About the Author
 
Part 1: Setting the Stage
 
Chapter 1: Mathematics for Teaching
What’s the Purpose of Learning Math?

 
The Development of Mathematical Reasoning

 
Spatial, Algebraic, and Statistical Reasoning

 
Major Strategies

 
Conclusion

 
Discussion Questions

 
 
Part II: Developing Additive Reasoning
 
Chapter 2: The Major Strategies for Addition
Additive Reasoning

 
Developing the Major Strategies for Addition

 
The Split by Place Value Strategy

 
The Add a Friendly Number Strategy

 
The Get to a Friendly Number Strategy

 
The Add a Friendly Number Over Strategy

 
The Give and Take Strategy

 
Comparing the Major Addition Strategies

 
Conclusion

 
Discussion Questions

 
 
Chapter 3: The Major Strategies for Subtraction
Developing the Major Strategies for Subtraction

 
The Remove by Place Value Strategy

 
The Remove a Friendly Number Strategy

 
The Remove to a Friendly Number Strategy

 
The Remove a Friendly Number Over Strategy

 
The Find the Distance/Difference Strategy

 
The Constant Difference Strategy

 
Comparing the Major Subtraction Strategies

 
Conclusion

 
Discussion Questions

 
 
Part III: Developing Multiplicative Reasoning
 
Chapter 4: The Major Strategies for Multiplication
Multiplicative Reasoning

 
Important Foundations

 
Developing the Major Strategies for Multiplication

 
The Smart Partial Products Strategy

 
The Smart Partial Products: Over Strategy

 
The Smart Partial Products: 5 Is Half of 10 Strategy

 
The Doubling/Halving Strategy

 
The Using Quarters and Scaling Strategy

 
The Flexible Factoring Strategy

 
Comparing the Major Multiplication Strategies

 
Conclusion

 
Discussion Questions

 
 
Chapter 5: The Major Strategies for Division
Important Foundations

 
Developing the Major Strategies for Division

 
The Smart Partial Quotients Strategy

 
The Smart Partial Quotients: Over Strategy

 
The Smart Partial Quotients: 5 Is Half of 10 Strategy

 
The Equivalent Ratios Strategy

 
Comparing the Major Division Strategies

 
Conclusion

 
Discussion Questions

 
 
Part IV: Putting It All Together
 
Chapter 6: Tasks to Develop Mathematical Reasoning
Sequencing Tasks

 
Problem Strings

 
Other Instructional Routines

 
Games

 
Hint Cards

 
Conclusion

 
Discussion Questions

 
 
Chapter 7: Modeling and Models
Strategies Versus Models

 
The Many Meanings of Model

 
Exploring Models by Their Best Uses

 
Our Modeling Framework

 
Conclusion

 
Discussion Questions

 
 
Chapter 8: Moving Forward
Mentor Mathematicians

 
Where to Start

 
Conclusion

 
Discussion Questions

 
 
References
 
Index

What happens when you shift math from being about rote memorizing and mimicking to focusing on strategies, thinking, and reasoning? There
is no one better than Pam Harris to guide you in this important path—and this one is for you, grade 3–5 teachers!

Jo Boaler
Stanford University
Stanford, CA

In this book, Pam Harris continues her quest to make math figure-outable—this time for grade 3–5 teachers. Through real classroom examples, Harris teaches us how addition, subtraction, multiplication, and division strategies should be experienced and understood, and she gives us the tools to teach these central ideas in mathematics.

Peter Liljedahl
Simon Fraser University
Burnaby, BC, Canada

Through extensive use of representations and illustrations, Pam Harris effectively illustrates how to develop reasoning strategies developmentally
across the operations. Smudge problems and number strings appearing throughout the book provide enriching ideas for how to help students make
sense of strategies and become reasoners. An excellent, practical resource for developing computational fluency.

Jennifer M. Bay-Williams
University of Louisville
Pewee Valley, KY

Pam Harris has done it again! Upper elementary teachers will be grateful to have this resource. Harris shares the why and the how to support students with developing mathematical reasoning so they can use mathematics to make an impact on the world. She offers practical strategies alongside examples from teachers and students engaging in powerful math experiences. This book will truly change the game as we build a community of Mathers together!

Deborah Peart Crayton
My Mathematical Mind
Charlotte, NC

Brilliant book—absolutely transformative! This comprehensive analysis delivers game-changing insights through its detailed examination of
strategies and models. Every section captivated me with thought-provoking content that shifted my perspective entirely. The fresh viewpoints sparked innovative ideas I’m excited to implement. From start to finish, this work combines depth with accessibility brilliantly!

Dr. Nicki Newton
Newton Education Solutions
Bridgeport, CT

Standard algorithms, those remnants of a pre-computing era that are often disparaged by regular people and math educators alike, remain quite common in school mathematics. Pam Harris not only critiques the standard algorithms but builds up worthy replacements with mathematical reasoning and big ideas to support student learning. Her expertise across grade levels has led to a fun and useful book series.

Samuel Otten
University of Missouri
Columbia, MO

Developing Mathematical Reasoning: The Strategies, Models, and Lessons to Teach the Big Ideas in Grades 3–5 offers a clear, well-structured progression of strategies designed to build deep conceptual understanding in the elementary classroom. Particularly noteworthy are the classroom vignettes, which vividly illustrate the real-world application of problem strings and rich tasks. These examples not only highlight effective instructional practices but also demonstrate how mathematical reasoning can thrive in diverse classroom settings.

Brendan Scribner
Scrib Mather, LLC.
White River Junction, VT

Pam Harris has always been competent and gritty about enhancing mathematical understanding. This latest book provides teachers with
invaluable strategies and insights, making it an essential resource for fostering critical mathematical reasoning in students.

India White
National Education Consultant
Tampa, FL

This book is a must-have for anyone teaching math differently than they learned it. It is deeply instructive, without being intimidating. The visuals, examples, and classroom-based vignettes deliver countless aha moments and deliver the ‘why’ behind the strategies and models. If math is something you’ve avoided, this book will give you the confidence you need!

Alison J. Mello
North Attleboro, MA

Another amazing Pam Harris book to add to your collection! She has created a comprehensive resource for ALL math teachers in grades 3 to 5.
This book covers what you need to know about teaching the major strategies for the main math operations, so that you can create a classroom that emphasizes thinking and reasoning every year.

Danika Murray
York House School
Vancouver, BC, Canada

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