I think a significant (maybe the most significant) factor that needs to be considered, is the quality of the teaching. I'm sure most people here had an experie

I think a significant (maybe the most significant) factor that needs to be considered, is the quality of the teaching. I'm sure most people here had an experience trying to understand a particularly difficult concept in Math class, staring at the equations spanning many pages, full of Greek symbols, feeling hopeless, only to have it explained by someone in a really intuitive way. When this happened to me I felt a combination of joy and frustration - if only every difficult topic could be presented in such an intuitive, way I could understand everything! Conversely my previous attempts at understanding the sea of Greek symbols on the paper was wasted effort, even after cracking the problem it didn't bring me closer to enhancing my understanding. The improvement was not a factor of time investment, or increased intelligence on my part