The late John A. Van de Walle was a professor emeritus at Virginia Commonwealth University. He was a mathematics education consultant who regularly gave professional development workshops for K--8 teachers in the United States and Canada. He visited and taught in elementary school classrooms and worked with teachers to implement student centered math lessons. He coauthored the Scott Foresman-Addison Wesley Mathematics K--6 series and contributed to the Pearson School mathematics program, enVisionMATH. In addition, he wrote numerous chapters and articles for the National Council of Teachers of Mathematics (NCTM) books and journals and was very active in NCTM, including serving on the Board of Directors, as the chair of the Educational Materials Committee, and as a frequent speaker at national and regional meetings. LouAnn H. Lovin is a professor of mathematics education at James Madison University (Virginia). She coauthored the first edition of the Teaching Student-Centered Mathematics Professional Development Series with John A. Van de Walle as well as Teaching Mathematics Meaningfully: Solutions for Reaching Struggling Learners (2nd ed.) with David Allsopp and Sarah Vaningen. LouAnn taught mathematics to middle and high school students before transitioning to PreK--grade 8. For almost twenty years, she has worked in PreK through grade 8 classrooms and engaged with teachers in professional development as they implement a student-centered approach to teaching mathematics. She has published articles in Teaching Children Mathematics, Mathematics Teaching in the Middle School, Teaching Exceptional Children, and Journal of Mathematics Teacher Education and has served on NCTM's Educational Materials Committee. LouAnn's research on teachers' mathematical knowledge for teaching has focused most recently on the developmental nature of prospective teachers' fraction knowledge. Karen S. Karp is at the School of Education at Johns Hopkins University in Baltimore (Maryland). Previously, she was a professor of mathematics education at the University of Louisville for more than twenty years. Prior to entering the field of teacher education she was an elementary school teacher in New York. She is also coauthor of Elementary and Middle School Mathematics: Teaching Developmentally, Developing Essential Understanding of Addition and Subtraction for Teaching Mathematics in PreK-Grade 2, and numerous book chapters and articles. She is a former member of the Board of Directors of NCTM and a former president of the Association of Mathematics Teacher Educators (AMTE). She continues to work in classrooms to support teachers of students with disabilities in their mathematics instruction. Jennifer M. Bay-Williams is a professor of mathematics education at the University of Louisville (Kentucky). Jennifer frequently offers professional development about effective mathematics teaching to K-12 teachers and leaders. She has coauthored numerous books, including On the Money: Math Activities to Build Financial Literacy; Mathematics Coaching: Resources and Tools for Coaches and Leaders, K-12; Developing Essential Understanding of Addition and Subtraction for Teaching Mathematics in PreK-Grade 2; Math and Literature: Grades 6-8; and Navigating through Connections in Grades 6-8 . Additionally, she has written dozens of articles on teaching and learning in NCTM journals. Jennifer serves on the NCTM Board of Directors, and has served on the TODOS: Equity for All Board, and president of the Association of Mathematics Teacher Educators (AMTE). Jennifer taught elementary, middle, and high school in Missouri and in Peru, and continues to work in classrooms at all levels with students and with teachers.