There was a study a while ago that found a correlation between book ownership in a child’s house and educational achievement. So some municipality (can’t remember which) kickstarted a program to mail a few age appropriate books to kids in their per month.

The result was no change. It turned out that the actual cause wasn’t books, it was parents who would value books enough to purchase them. Buying books for children whose parents hadn’t valued reading and education enough to already own some books didn’t help at all.