Want your children to go further in their education—high school, college, maybe more? Want them to earn more as adults?

Here’s one key predictor of educational attainment and earning power. Is it IQ? Is it economic status?

No, it’s the number of books in the home. That’s the finding of a 20-year study conducted in over twenty-seven nations and published in the June 2010 issue of Research in Social Stratification and Mobility.

The conventional wisdom among researchers has been that the education of parents was the key factor. But having as few as twenty books in the home can have a significant impact. Having five hundred books means children will on average pursue two to six years more education depending on the country.

Researcher Mariah Evans said, “You get a lot of ‘bang for your book.’ It’s quite a good return-on-investment in a time of scarce resources.”

What was the bang for the book in my household? I grew up in a home with books. Not a lot of books, but enough.

My brother and I had bookshelves above our beds, lined with a few dozen volumes. We had bookshelves in the basement holding mass market paperbacks and a few somewhat more sophisticated titles.

Andy Le Peau is Associate Publisher for Editorial for InterVarsity Press and this article first appeared in his blog, Andy Unedited

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