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> On a more meta level, it feels like we’ve barely touched the margins of how humans learn best. That’s always struck me as odd.

It's very well studied. I'd start by reading a cognitive science textbook and go from there. I have Cognition by Reisberg[0], it was well-written and well-structured.

Alternatively, an entertaining and informative popular account is Make It Stick by Brown, Roediger and McDaniel[1].

I do agree that the research findings are greatly underapplied, though.

[0] https://www.amazon.com/Cognition-Exploring-Science-Mind-Seve...

[1] https://www.amazon.com/Make-Stick-Science-Successful-Learnin...

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