Your followup question might be So how come he did badly at the Math courses the first time around? and my response is, he hadn't developed enough problem-solving skills yet. He'd run up against a tough example, try one or two ways to solve the problem, then give up. I'm going to try to stay on top of his progress this time, and make sure that he understands each week's work.

Personally I know loads of great developers who a lousy at maths, and a moderate number of great maths folks who are lousy developers. So I wouldn't worry myself.