Module 4 is devoted to three major areas of work. The first two are building fluency in two-digit addition and subtraction within 100 and applying that fluency to one- and two-step word problems of varying types within 100. Students’ increasing fluency with calculations within 100 allows for word problems to transition from being mere contexts for calculation into opportunities for students to see and analyze the relationships between quantities. Daily Application Problems and specific lessons in Topics A, C, and F provide students with guided and independent practice as they solve a variety of problem types, including more complex comparison problems. Note that most two-step problems involve single-digit addends and do not involve the most difficult comparison problem types.1 The third major area of work is developing students’ conceptual understanding of addition and subtraction of multi-digit numbers within 200 as a foundation for work with addition and subtraction within 1,000 in Module 5.