Without reading the books, my initial take is that this is not inconsistent with Judith Rich-Harris' claims that nurture by itself is a poor lever of influence over how kids turn out. The fact is that some kids, in some schools do phenomenally better than other kids in other schools. Ironically, the fact that schools and peers care enough to assign it might be more important than the homework itself. From the review:
"It has been drilled into our collective psyche that rigorous schools assign rigorous homework," [a school principal] wrote. "I recognize that this is a ridiculous thought process, particularly since your research suggests otherwise, but it's hard to break the thinking on this one. How could we be a high-achieving school and not assign homework?"