I don't think it's really necessary to know how people learn because I don't think that everyone uses the same method. We all have different methods of learning. For example, some people memorize information, others like to learn in practice, some people have good picture memory and so forth.
It's much easier to see how a teacher is teaching and how effective it is. It's not too difficult to measure this. If students get better grades and learn better with the use of instructional exercises for example, we know that this is a method that works.