[TZubiri]

Cost is a huge factor. Asking a student to write what 7+8 is on a sheet of paper is a cheap substitute of high quality math education.

Not saying that this is the case in OP, it's very likely that the teacher will eventually catch up to the fact that a kid with A on their homework isn't quite a math genius. The same systems that would catch a child being aided by parents or cheating would catch this anomaly.

Teachers are a well trained profession after all.