He could try the Art of Problem Solving Prealgebra videos (http://www.artofproblemsolving.com/Videos/index.php?type=prealgebra) and on-line problem program, Alcumus (http://www.artofproblemsolving.com/Alcumus/Introduction.php). Ideally, this can be done along with their text, though I see nothing wrong with playing around on Alcumus without it, to see if he likes it.