Different people learn different things in different ways. Some people learn by listening to lectures and teachers, some by reading and self-study, and some by either doing or trying out things for themselves or in an apprenticeship sort of a setting.
Children mostly learn by either listening or doing things for themselves since their reading comprehension faculties would not have developed sufficiently. It is probably around the age of 12–13 when the reading comprehension of most kids develops sufficiently to enable self-study. So kids who previously found it hard to listen and learn from their teachers in a classroom setting begin to self-study, discover things for themselves, find subjects they are interested in, and start doing well in them. So there is a lot of diversity in student temperament.
Learning and teaching, too, often exhibit diversity. Learning and pedagogy can usually be cast into this 2-d space of learnability and teachability of a subject.
Some subjects are more suited for self-learning and MOOCs, like picking up a new programming language; there are other subjects where having a teacher or apprenticing under someone can be very useful — like picking up the ropes for a career in academia through graduate education. So, just like student temperament, there is diversity in the nature or characteristics of the subject being learned or taught.
An education system and a pedagogical culture that does not account for this diversity in student temperament and subject characteristics will result in many students falling through the cracks of the system.