I would agree with Ania about staying away from formal text books. If your child is on the verge of being turned off by math, then you don't want to just give him more of the same. Math can be very playful and most of the true mathematicians I have known love to play with ideas as well as numbers. What it seems like one would want is to have a mentor who can help introduce a playful element to math (something which most elementary school teacher leave out, often because of their own insecurity with the subject). Real world problems and puzzles (especially ones with multiple solutions) would be a good place to start.
