The Ray's Arithmetic series begins at a preliterate level with counting; then takes the child through addition, subtraction, multiplication, division, and so upward until calculus, teaching concepts with thorough explanations followed by ample problem sets. The Ray's series provides a very full-bodied course of mathematics.
I love Ray's Arithmetic because it focuses on mental math and uses an abundance of word problems, teaching children the practical use of math.
You can get it here for free.
