Great way to practice and track student progress over math concepts and much more.
Community Review for Khan Academy
My Take
It has videos on almost any concept you could think of across the all curriculums, but the the math exercises and the section on learning to program are the two best features for classroom learning. There are over 400 math concepts that students get to practice from learning to tell time all the way up to the very basics of calculus. They have added some additional cool features that no allow a coach to recommend lessons which was not available as of spring 2013. Students like the points and badges that they could earn, they would get immediate feedback on the problems they missed, and you could easily track student progress and class progress though the tools that are available to a "coach". The one downside I have found is that some of the problem sets would become repetitive and ask the same problem 2 or 3 times per set of 8 questions. Students could work on problems from either a computer or mobile device and there is a way to work out the problem with in the browser using ink tools within the work space.
How I Use It
I have helped teachers set up their students in the classroom and it was used as a practice sessions and remediation for students who were struggling and it allows the teacher and parents to track how their student is doing. As a "coach" I am allowed to see how many problems a students worked on per concept, how long they worked on each problem, and which problems they missed. Students could become bored with this if used too often so I would limit it to 10 to 20 minutes once or twice a week during school hours or have them do it as part of their homework.