^{(I was inspired by the comments in this answer to ask this question.)}

I have some multiplication table cards from Kumon that have a list of commonly mistaken multiplications: $7\times 8,4\times 8,11\times 12,7\times 9,6\times 7,12\times 8,4\times 7,6\times 8,9\times 12,8\times 9,11\times 11$, and $6\times 9$ (in this order).

I assume that this is based on data they obtained from the numerous children who have answered their worksheets.

Is there some other source (a study, perhaps) that lists the products of single digits that children usually get wrong?