| The first two paragraphs illustrate a huge problem with US math education, which pre-dates common core, but is reinforced by it. That problem is the false belief that numeracy is improved by learning different ways of looking at number operations. (i.e. four ways to subtract). Our child's second-grade teacher (a very good teacher) has a poster illustrating 7 ways to subtract. Seven ways, no exaggeration. This poster is older than common core. Students learn math just like they learn to kick a ball. By practicing. Learn one way to subtract, and practice it really really well. Or learn two ways, and practice each way really, really well. Learn more ways if you want, but practice each way really really well. Most math curriculums assume that learning multiple ways is equivalent to (or better than) practicing one way. They don't require the repetitive practice. As comments have pointed out, the common core standards don't explicitly require this multi-way approach. But the CC standards compound the problem by requiring students to explain concepts in order to demonstrate mastery. Completing lots of subtraction problems with a low rate of error doesn't count. You must explain, in order to understand. And if you really understand, shouldn't you be able to explain different approaches? I would say no. Or at least, not yet. I don't want a third-grader explaining how to subtract unless they can also finish 50 subtraction problems in a row without pausing to struggle. And if they get the problems right? Good job, you get an A. Wonderful, let's skip grading the explanation because that is subjective as hell. TL/DR: The article rightly points out a crap way to teach math. Common core is not totally to blame, but it makes a bad problem worse. |
There's no strong reason to glorify one particular subtraction algorithm over another, especially since the actual use case for it is relatively rare.