This chapter begins with a discussion of what it means to promote reasoning and sense making. It examines the teaching of number sense and algebra. Instead of viewing “number sense” and “algebra” as courses to be taken in secondary or middle schools, the Common Core State Standards for Mathematics (CCSSM) views them as content strands—topical areas to be revisited and further developed each year that a student attends school, from kindergarten through the senior year of high school. The spirit of the CCSSM is that content areas such as number and algebra are revisited throughout a student’s mathematics education although the relative emphasis of the topics varies across the years. A standard deck of playing cards can be used for students to practice their skills with positive and negative numbers. A topic such as algebra becomes increasingly important as students move from elementary into the middle and secondary grades.