I've recently fallen in love with Art of Problem Solving, which sounds like it might be of interest to several of you if you haven't seen it. Math, by mathies, for mathies. Very visual, everything derived from first principles, tons of depth and complexity rather than drill.
There's an on-line data base (free) of problems which covers full courses, including pre-algebra and algebra, which could be a good way of finding those holes as well as covering material in a fun way. There's (free) videos that go with a number of courses, textbooks, and actual courses (expensive).
We've just completed pre-algebra on our own using AoPS textbook and online database questions ("Alcumus"); I've loved the book, videos and Alcumus. In a couple of weeks, DS will start Algebra I as formal AoPS on-line course, so can't speak to that experience yet.
AoPS won't replace a human tutor, but could be really useful both to fill gaps and offer challenge. The AoPS on-line community is huge and also a big draw for many. For a kid who is visual and likes the conceptual side of math, a great experience.
Hope this is useful - and good luck!
