[tokenadult]

I'm looking for a reference for the point, and my keyword searches on Google have yet to take me to the right place, but I recall that research has shown that gifted students actually have learning GAINS when they are out of school during summer, but then the school year begins with review of the material that other students didn't learn even during school the year before. So one strategy to make the time that children spend in school more worthwhile would be to let learners advance at their own pace, and not put all learners into lock-step grades in school by age.

http://learninfreedom.org/age_grading_bad.html

We don't group students by height, or by weight, or by social maturity, or by sports skill, so there isn't any good basis for grouping them by age when we could group them by achieved subject-matter level, and have each class in each subject proceed through the lessons just as rapidly as learners can with the best matching instruction.