Hi!
I have taught all levels of math over the years, well, secondary levels.
You don't mention what age level you're interested in. But from what I have seen, there is a lot of good computer software out there which covers basic concepts in math. It allows underachievers to work on similar types of problems at their own pace. And usually the material is presented as a game so that the student is not bored practicing basic arithmetic skills. If you can find the "fun" software in math, then I would recommend using it. Years ago, one company called Sunburst produced some very good programs of this kind. I am not sure if they are still in business. Probably they are.
I would check with your math department chair or if you are in grammar school, call up the department chair over at the nearest junior high or high school and ask them for suggestions.
Regards,
Allison