There's no dispute that students differ in aptitude for subjects. Where things get more complicated is when you view this in terms of other variables like time.

There's no dispute that students differ in aptitude for subjects. Where things get more complicated is when you view this in terms of other variables like time. Do some students eventually get better than others, say start off worse but end up becoming better (a sharper trajectory)? If so, at what point do we deem a student's aptitude to be better than another student's, or should this always be a time-varying function? Do certain subjects which become more important due to technological or social changes, like say computing, benefit a student who otherwise would not have shown a talent in anything taught in a school? Donald Knuth was a history major in school originally. I think there will always be really good and really bad students in every subject. The hard part is everyone else.