Subtraction skills tend to be more difficult for students to develop when compared to addition. To be good at addition students, need to know the number order, e.g., 11 + 5 sounds like 11, 12, 13, 14, 15, 16.
To do well with subtraction, students need to have hierarchical inclusion. Hierarchical inclusion includes knowing what numbers are embedded within another number. Students need to know and have multiple experiences counting and decomposing 12 into (11, 10, 19, 18, 7, 6, 5, 4, 3, 2, 1). To subtract 12 – 7 = efficiently, students must know that counting up to 12 from 7 (8, 9, 10, 11, 12) will get them to the final answer.
It is also helpful if students are comfortable counting backward from any given number. Counting collections is the perfect opportunity to develop hierarchical inclusion and the skill of counting backward. Try listening to a few of your students count out loud backward this week.