My fourteen year old was rusty on a concept he needed to know for his Art of Problem Solving math class. I told him to go watch the Khan Academy video. Despite my recommendations to use the site before he barely has used it.
My older son found the video helpful. He noticed the login and how it can track the progress if you do problems online (like the Alcumus part of the AoPS class and also like Aleks math). He asked if he could try it and I said yes, if he opens a gmail account. So he did. He spent about two hours doing math problems. Their frequent awarding of badges and achievements is something that he really likes ("just like xBox360 game achievements").
Last night he started telling his younger brother about it and then older brother showed younger brother how it works. They also noticed you can login with your Facebook account. Then I was asked if they could set up an account for my younger son. They got sucked in and I had to boot them off the computer at nearly 10 p.m. since my younger son loved it so much.
Today my younger son asked if he could begin doing math with Khan Academy instead of Teaching Textbooks 7 which has too much frustrating review. Perhaps one of their favorite things about it compared to other programs is you don't feel penalized for life with a bad grade if you make a data entry error with your answer. Khan Academy just gives you more problems to solve and when you have solved a certain number, a streak of 10 or 20 (up to 100) then the labeling system they use on you looks like a success rather than a permanent low number grade due to a past error.
In fact if the goal is to learn, and the student does learn, then they should get a passing grade rather than being graded on every single problem they do for practice (not just being graded on tests or quizzes). The downside of Teaching Textbooks is there is a low number of problems in each lesson and even a slip of the finger on the keyboard scars you for the entire school year with a lower grade. Yes, you get two times to enter the response but for whatever reason my kids have the right answers on paper but screw up on data entry more times than any person would think a person could.
Khan Academy uses video clips that show the math problem being worked with teacher explanation with audio sound to teach a short lesson. If you login you can do problems and record answers. A map shows your progress. The system also figures out what topics you may bypass due to showing mastery of concepts.
Khan Academy is free of charge.
Khan Academy also has high school and college level economics, finance and science topics.