Schaum's outline series I would recommend for doing.
Any book on calculus. Any book on differential equations. Any book on linear algebra. Any book on abstract algebra.
There are plenty of good lecture series on-line if you have the patience from leading universities. MIT opencoursewear is particularly popular these days, but it's not necessarily the best. Watching them is more likely to make your son curious/give confidence than actual skills, but that could be said to be useful, especially over long blocks of time.
I'll ignore the 'pure' maths bit lol.
For the course listed it's all a bit vague, but likely to cover some of the stuff ^^.
Maths courses are very varied the higher you go, I still get snidey comments from lecturers/on-line from people who really should know better 'yeah, but I find it very surprising an undergraduate would have studied that and have that level of knowledge'. Yes, well be bloody surprised.