1.OA.C.6

Add and subtract within 20, demonstrating fluency for addition and subtraction within 10. Use strategies such as counting on; making ten (e.g., 8 + 6 = 8 + 2 + 4 = 10 + 4 = 14); decomposing a number leading to a ten (e.g., 13 - 4 = 13 - 3 - 1 = 10 - 1 = 9); using the relationship between addition and subtraction (e.g., knowing that 8 + 4 = 12, one knows 12 - 8 = 4); and creating equivalent but easier or known sums (e.g., adding 6 + 7 by creating the known equivalent 6 + 6 + 1 = 12 + 1 = 13).

Subtract by making tens. For example, 13 - 4 = 13 - 3 - 1 = 10 - 1 = 9. Then practice counting on, adding by making tens, and subtracting by making tens. Add within 10 by adding on to 5, as seen here. This is useful because students can quickly count within 10 by subitizing five, then adding on. I often do this myself when counting a number of objects within 10. Conclude by giving this challenge. A couple additional questions can be found here.

Notes: This standard is too vague. Exactly which methods should they be using? For example, can they add and subtract with a number line, or is that not considered fluent?