I'll bet you equally good correlations can be found when the parents have a Kindle library that the kid doesn't have access to. You'd expect articles like this

I'll bet you equally good correlations can be found when the parents have a Kindle library that the kid doesn't have access to. You'd expect articles like this to have a paragraph, "The researchers controlled for biological heredity by ________" but it seems they don't want you to take them seriously. Edit: Oh, they also show that growing up in a home full of books makes you more numerate, too. So, no surprise, there's a general intelligence factor involved that has nothing to do with books.