Comment by ivan_ah

There is no grand theory perhaps, but educational research is not totally useless, people have accumulated a lot of insights over the years and some of these "intuitions" are also backed by studies.

Here are some book-length reviews of currently known things about learning/teaching that I found to have a very high signal-to-noise ratio:

https://www.routledge.com/How-Learning-Happens-Seminal-Works...

https://www.routledge.com/How-Teaching-Happens-Seminal-Works...