First, students will learn how to add within 20. One method, is to add by counting forwards, starting from the first addend. Another method, is to add by making tens. For example, 5 + 9 = 4 + 10 = 14.
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Next, students will learn how to subtract within 20. One method, is to subtract by counting backwards, starting from the minuend. Another method, is to subtract by making tens. For example, 13 - 4 = 10 - 1 = 9.
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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?
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).
1.OA.C.5: Relate counting to addition and subtraction (e.g., by counting on 2 to add 2).