The Best Kids’ Books Ever -- Summer Break and IQ
nytimes.com
nytimes.com
A really good book for a teenager would be The Chosen by Chaim Potok,
http://www.amazon.com/Chosen-Chaim-Potok/dp/0449213447/
which I think I read at age fourteen. It's an excellent story about two very bright boys growing up in Brooklyn during World War II.
The way you phrase that makes it sound like there are studies that show this. Do you know of any, or are you just saying that was true for you and others you know?
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.
That being said, my babysitter growing up lived in the woods... we ate bear stew for most dinners... and they only rented me horror movies. I saw all Nightmare on Elm Street and Friday 13th movies by the time I was about 8. Yeah, I had some twisted nightmares once in a while, but I think most kids do anyhow, and... I turned out alright!
But while on the subject, the Percy Jackson series by Rick Riordan is a great choice with both genders and is great fun for adults too.