I guess you're studying "Erziehungswissenschaften"? You might find that educational psychology ("Pädagogische Psychologie") has a lot of the depth you would expect. One nice example is cognitive load theory.

One of the more complex mathematical treatments of learning are "knowledge and learning spaces". But it seems they get bogged down a lot in implementation details (= conflating implementation with interface behaviour). And: It's a bit to simplistic. For example, talking about things like the "expertise reversal effect" in this framework is not straightforward.