The impression I get from his discussion of the French & Russian elite schools is that the summer courses may be better considered part of the filter for admission into those sort of schools; specifically, footnote #150:

Agreed that seeing someone in class is useful information, and that this is a good feeder system for elite schools. But to the best of my knowledge there is not a quality national network of elite math and science schools in the US, just a collection of local magnet schools.