I agree -- even teenagers' brains are not yet fully developed, and they often make rash, emotional decisions that aren't in their best interest. Further, our compulsory school requirement provides a lot of benefits and protections to children who may have parents that would neglect their education, and it ensures at least one good meal a day.
Still, I think this piece presents some interesting ideas, and I think that the freedom to quit could be extended to schoolchildren, perhaps by allowing them more leeway in their choice of classes or assignments.