That happens all the time. If I can catch them in grade two or three and correct some of their number-sense issues then, they've got a much firmer base to learn everything that's going to come after it. But if they get past grade three without understanding such basic concepts as ordered pairs to ten and twenty, it's much, much harder to bring them up to speed later.

I think a huge part of the math deficit in North American education comes about because don't go all-out to bring kids up to speed on those basic concepts in primary, so the problems just get worse in junior and intermediate until you have a high school student who not only lacks the background knowledge for the course, they lack the background knowledge right back to grade two and furthermore, are convinced they're dumb because of it.