My plan for the summer is to have DD do Khan Academy, which is free and includes video lessons of the concepts, and supplement with something like Singapore math to reinforce those concepts. My goal is to close gaps so that she can go straight from third grade math to fifth or sixth grade math, since she already knows most of the 4th-5th grade level material. Some people have argued that Khan Academy is just teaching numerical operations, but I don't agree. For the lower grades at least, I think he is pretty good at explaining why math is done the way it is. For instance 7/8 is the same as 7 X 1/8 and why. Then kids understand why fractions can be multiplied the way they are. It never would have occurred to me to explain it that way, I would have just said "multiply the top numbers, then the bottom numbers."
With Khan Academy, I go to the specific grade level we are working in and have my kids work their way down the list of skills. It does quiz the kids on each concept and they have to get 5 in a row correct.
