Khan Academy now have on the order of 2,200 videos covering everything from basic arithmetic all the way to vector calculus . They have a million students a month using the site, watching on the order of 100 to 200,000 videos a day.
These resources can be very effective as revision or reinforcement tasks, a backup for students who miss a lesson or for students who need further input to fully understand certain concepts.
Salman Khan: Let's use video to reinvent education | Video on TED.com
See what is available:Browse the library
Start at the very beginning. The software will build your streak. It builds profiency with unlimited problems until you get 10 in a row, in a game like framework. Students can earn badges to encourage and motivate them.There are hint facilities available and the software allows students to work at their own pace. There is plenty of feedback for teachers and parents to view. These resources should be used as part of a balanced course.