[cicatriz]

Not sure how deep down the rabbit hole you want to go, but here's what I know:

The field of intelligent tutoring systems is essentially how to break up a problem and estimate your knowledge on each piece (called a "knowledge component"), and then how to instruct based on the resulting student model. I got started by reading about Andes physics tutor: http://oli.cmu.edu/wp-oli/wp-content/uploads/2012/05/VanLehn... but there are many examples.

Most of the research doesn't actually incorporate spaced repetition. One exception is Philip Pavlik's work: http://optimallearning.org/

It's still a lot of effort to break things down into knowledge components and figure out the sequencing and instruction. That's why companies like Carnegie Learning and Knewton exist, and even those are only targeting elementary or intro level material for now.