Salman Khan of the Khan Academy says it best.
People learn at different rates. Some people seem to catch on to things in quick bursts of intuition; others grunt and grind their way toward comprehension. Quicker isn’t necessarily smarter and slower definitely isn’t dumber.
Further, catching on quickly isn’t the same as understanding thoroughly. So the pace of learning is a question of style, not relative intelligence. The tortoise may very well end up with more knowledge—more useful, lasting knowledge—than the hare…whether there are ten or twenty or fifty kids in a class, there will be disparities in their grasp of a topic at any given time.
Even a one-to-one ratio is not ideal if the teacher feels forced to march the student along at a state-mandated pace, regardless of how well the concepts are understood.
–The One World Schoolhouse: Education Reimagined by Salman Khan