That is a form of "mastery-based" learning. Basically, you group students according to ability and separately teach them each topic to the point of mastery befo

That is a form of "mastery-based" learning. Basically, you group students according to ability and separately teach them each topic to the point of mastery before moving onto the next topic. The guy from the Khan academy talks about that (https://www.youtube.com/watch?v=LnVzug0mA2w https://www.youtube.com/watch?v=LnVzug0mA2w), although he suggests going even further-- individualizing each student. BTW, this is how the children of very wealthy parents often get to elite colleges in quite high numbers. The parents send them to private schools where student-teacher ratios can be as low as 5 (FIVE!). Under those circumstances, each student can get tracked very accurately according to their needs and aptitudes. It is a great way to learn, it works, but is also very expensive.