I read that book, and Paul Tough explicitly says that the HCZ school programs aren't designed based on research, and there is little evidence to suggest that their pedagogy is sound.
He does have more praise for the curriculum of Baby College, but that is completely different.
School can dumb you down.
It seems that it can also smarten you up.
See:
hcz.org/our-results
And the book Whatever It Takes by Paul Tough.