"When for children it is also the time in which they develop socially."

I've seen this argument many times, but it has never seemed persuasive.

Where else in life are you ever going to encounter an environment where all the other people are within 12 months of your age, except for the authority figure up front? Other than maybe military bootcamp, never. Even prison has a range of ages and backgrounds represented.

The social skills learned in such an artificial environment are highly unlikely to transfer to the real world.