Susan Janssen Creighton is a senior mathematics associate at Education Development Center (EDC) in Massachusetts. She has worked in mathematics education for 30 years, both in schools and at EDC, where her work has focused largely on K–12 mathematics curriculum development and mathematics teacher professional development. Currently, her work focuses on helping mathematics teachers adopt and successfully implement formative assessment practices, and on supporting teachers’ understanding and use of the CCSS Standards for Mathematical Practice. As a member of the NSF-funded project, Formative Assessment in Mathematics Classrooms: Engaging Teachers and Students (FACETS), she was a lead facilitator for several of the participating districts. Creighton has written print and online materials for numerous clients, including the international Department of Defense schools, the Columbus, Ohio public schools, the National Board of Professional Teaching Standards, Everyday Learning publishers, the PBS TeacherLine project, the Massachusetts Dept. of Education, and the E-Learning for Educators project funded by the U.S. Dept. of Education. She has also served as the director of the MathScape Curriculum Center, a national center that supported the implementation of the NSF-funded mathematics curriculum MathScape developed at EDC, for which she was also one of the writers, and has led numerous teacher professional development opportunities for middle and high school teachers on the teaching and learning of mathematics. Prior to coming to EDC, she taught middle school and high school mathematics for a number of years in Portland and Saco, Maine and in Brookline, Massachusetts.  She received a B.A. mathematics and a M.Ed. in Secondary Education, with a concentration in curriculum, both from the University of New Hampshire. She currently lives in western Massachusetts with her husband, her two teenagers, and the world’s softest dog. Cheryl Rose Tobey is a senior mathematics associate at Education Development Center (EDC) in Massachusetts. She is the project director for Formative Assessment in the Mathematics Classroom: Engaging Teachers and Students (FACETS) and a mathematics specialist for Differentiated Professional Development: Building Mathematics Knowledge for Teaching Struggling Students (DPD); both projects are funded by the National Science Foundation (NSF). She also serves as a director of development for an Institute for Educational Science (IES) project, Eliciting Mathematics Misconceptions (EM2). Her work is primarily in the areas of formative assessment and professional development. Prior to joining EDC, Tobey was the senior program director for mathematics at the Maine Mathematics and Science Alliance (MMSA), where she served as the co–principal investigator of the mathematics section of the NSF-funded Curriculum Topic Study, and principal investigator and project director of two Title IIa state Mathematics and Science Partnership projects. Prior to working on these projects, Tobey was the co–principal investigator and project director for MMSA’s NSF-funded Local Systemic Change Initiative, Broadening Educational Access to Mathematics in Maine (BEAMM), and she was a fellow in Cohort 4 of the National Academy for Science and Mathematics Education Leadership. She is the coauthor of six published Corwin books, including seven books in the Uncovering Student Thinking series (2007, 2009, 2011, 2013, 2014), two Mathematics Curriculum Topic Study resources (2006, 2012), and Mathematics Formative Assessment: 75 Practical Strategies for Linking Assessment, Instruction and Learning (2011). Before joining MMSA in 2001 to begin working with teachers, Tobey was a high school and middle school mathematics educator for ten years. She received her BS in secondary mathematics education from the University of Maine at Farmington and her MEd from City University in Seattle. She currently lives in Maine with her husband and blended family of five children. Eric Karnowski is a senior mathematics associate at Education Development Center (EDC) in Massachusetts. He has worked in mathematics education for 25 years, initially as a teacher, then as a textbook editor, and finally as a curriculum developer and teacher professional development provider. Since joining EDC, he has directed the development of the K–5 program Think Math! and written numerous activities for the award-winning Problems with a Point website. He directed projects to develop several online teacher professional development courses for PBS TeacherLine, Louisiana Algebra 1 Online Professional Development, and most recently, the National Board of Professional Teaching Standards in both mathematics and science. In addition, he was a contributing author on Ways to Think about Mathematics and the MathScape curriculum. Prior to joining EDC, Karnowski had the distinct privilege to edit influential secondary textbooks for Janson Publications and Everyday Learning, including Contemporary Mathematics in Context by the Core-Plus Mathematics Project, Contemporary Calculus by the North Carolina School of Science and Mathematics, and Impact Mathematics by EDC. He received a B.S. in Liberal Arts (honors mathematics) and an M.S. in Mathematics, both from the University of Tennessee, Knoxville. He currently lives in Boston with his husband, Mark, and two large cats, Endora and Tabitha. Emily R. Fagan is a senior curriculum design associate at Education Development Center (EDC) in Massachusetts where she has developed print and online curricula as well as professional development and assessment materials in mathematics for fourteen years. She was Director of the MathScape Curriculum Center, a project funded by the National Science Foundation (NSF) to support schools, districts, and teachers in curriculum implementation, and she directed the revision of MathScape: Seeing and Thinking Mathematically (McGraw-Hill, 2005). She was a developer and facilitator of three NSF-funded projects, Addressing Accessibility in Mathematics and Differentiated Professional Development: Building Mathematics Knowledge for Teaching Struggling Students (DPD) aimed at supporting struggling math learners, particularly those with learning disabilities, and Formative Assessment in the Mathematics Classroom: Engaging Teachers and Students (FACETS) the inspiration for this book. Fagan is the co-author of two books:  Uncovering Student Thinking About Mathematics in the Common Core, Grades K-2 (2013) and its companion for grades 3-5, as well as book chapters and articles about curriculum implementation and instruction. Prior to joining EDC, Emily taught high school and middle school mathematics in Philadelphia and in Salem and Brookline, Massachusetts. She was a mentor teacher, math coach and member of the Massachusetts faculty of the Coalition of Essential Schools. She has long been interested in accessibility in mathematics education and improving opportunities for all students to learn and love math. While mathematics has been her focus for the last two decades, she has also taught science, social studies, and Spanish. Fagan holds an AB cum laude from Harvard University. She lives in Sudbury, Massachusetts, with her husband and their two children.