My 8 yo is doing BA and I would say that the hardest thing about it is sticking with the harder problems. The hard ones are hard -- even for me. Not the math, per se, but it is more like they are logic puzzles. My son sometimes gets fidgety and gives up. From what I understand, part of the BA approach is asking kids to sit and struggle with tough problems. It is less about finding the right answer.
Dreambox.com might be worth exploring. We have used it for years and I find it quite conceptual. It is pretty good at finding a kid's level and continuing to present material that is right at their learning edge. Both my kids find that there is a bit too much repetition needed, but on balance I have been happy with it.
