Missing from the four methods: borrowing and carrying numbers. You know, the old-fashioned-taught-the-same-way-for-decades-granny-method-not-approved-by-bureaucrats subtraction.
According to this third-grade textbook, students must take about six steps (at minimum, depending how you count) to subtract just two numbers. And if you don’t show your work, circle the right numbers and “count up” correctly, you haven’t proven that you’ve mastered the “why” of the problem.
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