The 170 lessons in Grade 2 are bound in four workbooks. Unit 1 reviews addition and subtraction facts through 10, and other skills taught in Grade 1. Unit 2 teaches all the addition and subtraction factions for the 11s, 12s, and 13s, and carrying and borrowing as well. Unit 3 teaches the 14s and 15s, and Unit 4 teaches the 16s, 17s, and 1