In a traditional classroom, the spread between the fastest and slowest students grows over time, [and so] putting them all in one class cohort eventually makes it exceedingly difficult to avoid either completely boring the fast students or completely losing the slow ones. Most school systems address this by... putting the "fastest" students in "advanced" or "gifted" class... and the slowest students into "remedial" classes. It seems logical... except for the fact that it creates a somewhat permanent intellectual and social division between students.