Without numbers and studies, this sounds like self-selection to me - people doing Khan Academy courses are surely more self-motivated than people attending coll

Without numbers and studies, this sounds like self-selection to me - people doing Khan Academy courses are surely more self-motivated than people attending colleges and universities, a substantial percentage of whom probably don't really enjoy being there. Spaced repetition and spacing effect is well known science and it works. For everything else I said, there should be more studies and experiments.