I encourage you all to see if you can get into workshops led by this group -- the Flipped.edu group. They are super K-12 teacher friendly and impressively leading edge -- and fun.
Math explained in easy language, plus puzzles, games, quizzes, worksheets and a forum. For K-12 kids, teachers and parents. The appearance makes it look like it's for a younger audiende, but some of the content is a nice suppliment to High School material.