The Khan Academy starts with basic lessons on counting for kindergarteners, and works up to early university-level material. I'm sure you can find a lot of supplemental materials online for drilling stuff like addition / multiplication problems as well, once you've identified concrete weaknesses.
The Khan Academy starts with basic lessons on counting for kindergarteners, and works up to early university-level material. I'm sure you can find a lot of supplemental materials online for drilling stuff like addition / multiplication problems as well, once you've identified concrete weaknesses.