What sort of substantiation were you looking for? The article pretty clearly states that the claims about the effects of the camp were based on exit surveys, and that the impact of the camp is demonstrated by the projects the camp grads are now working on. You could debate whether those are good measures, but we don't exactly have better ones.

I agree it would be nice if we could come up with standardized tests for rationality and then test whether camp attendance improves scores, but even if this were possible it hardly seems the best conceivable use of SIAIs resources.