If our homeschooling family gets asked anything most often it's, "What do you use for math?" Our three oldest children use the free math program at Khan Academy. They move through the program at their own pace. We use this instead of textbooks!
The program begins with basic addition. You must complete a streak of 10 correct answers before moving on to one of the next concept choices. At any time, you may view one of the suggested videos in which Khan explains the math concept. Your Knowledge Map (shown below) illustrates your student's progress.