Thanks, RSM looks good but I'm not really looking for a program that's a regular math class because I think my son will have his hands full with being in middle school. I'll have to revisit it if he settles in and actually does his school homework responsibly (doubtful)!
I'm more looking for something he can do for fun when he wants to (not much of a time commitment) where he'll learn something kind of parallel to the usual math sequence. He does math for fun, but we're running out of fun things for him to do that I know about. He likes math contest problems okay but not especially, and the local math circles seem to emphasize problem-solving. Like, he would be more interested in talking about how calculus was invented and why it works, or election paradoxes, or graph theory.
