Parental contribution is mainly genetic

Bryan Caplan argues that reading helps kids more than anything:

The big result is the lack of results. Controlling for family and child background, time in school and studying barely help - and television viewing barely hurts. Contrary to wishful assertions that exercising the body improves the mind, sports don't matter either. Out of nineteen activities, only two predict greater academic success across the board: reading and visiting.

The estimated effect of visiting is modest. Reading, however, is a huge deal.

Visiting refers to certain organized out-of-school activities.

A Nature study reports:

Meta-analysis of the heritability of human traits based on fifty years of twin studies

Despite a century of research on complex traits in humans, the relative importance and specific nature of the influences of genes and environment on human traits remain controversial. We report a meta-analysis of twin correlations and reported variance components for 17,804 traits from 2,748 publications including 14,558,903 partly dependent twin pairs, virtually all published twin studies of complex traits. Estimates of heritability cluster strongly within functional domains, and across all traits the reported heritability is 49%.

You can download the full article here.

People think that kids are shaped by schools, TV, parenting, etc. The data says that these things matter less than you think.

Saying that heritability is 50% makes it sounds as if parenting and schooling are the other 50%. But other studies show that the other 50% is mostly measurement error and unkown factors, as the measurable aspect of the environment seem to have very little effect.