I think it is a replicated result among students of gifted students that they GAIN ground intellectually during the summer school vacation, because they pursue

I think it is a replicated result among students of gifted students that they GAIN ground intellectually during the summer school vacation, because they pursue their own intellectual interests by independent reading and aren't slowed down by the school curriculum. Malcom Gladwell cites something similar in his book, Outliers - a study which showed that economically advantaged (high SES) kids progress in reading/math skills over the summer, while low SES students either stay within similar scores or score worse on reading/math tests over the summers. And by "something similar", I suppose I mean "the exact opposite" - kids whose parents engaged them in academic activities over the summer gained intellectually, while those left to "pursue their interests without a curriculum" fell behind.