Also, I think the concern about learned underachievement has nothing to do with "they might have cured cancer" and more to do with spending eight hours a day learning to underachive, and restricting goals to social skills like "doing boring work", while other kids are learning to and better themselves by learning, advancing, and developing.
But those are just thoughts and the reality is many brilliant kids grew up in public school anyway, and the results have varied by individual.

Youth lives by personality, age lives by calculation. -- Aristotle on a calendar