Tim H.

I have used Khan for science courses including biology, chemistry, and anatomy and physiology on the university level and am very satisfied with the layout and length of the videos and problems. My kids use it as their primary source of math education as homeschoolers. Sequential learning experiences for FREE to anyone are provided for learning of many subjects. Khan Academy focuses on understanding requiring few problems, but mastery which I prefer over multiple problems of "busy work." There is also an option to "test out" of material already mastered. We find the site exceedingly helpful.