The article doesn't mention anything about what the researchers controlled for. Some other explanations that fit the data: 1. Parents who take good care of the

The article doesn't mention anything about what the researchers controlled for. Some other explanations that fit the data: 1. Parents who take good care of their children in other ways also tend to read to their children (perhaps because they're conscientious and have read other research that says reading helps brain development, so they read to their kids). It's actually the "take good care of their children in other ways" that makes the difference, and reading just correlates. 2. There is a shared genetic factor between parent and child. Parents with this factor are more likely to read to their children. Children with this factor score better on literacy tests. Any factor that affects intelligence or personality would fit the bill. 3. Reading doesn't affect language skills, but they are instead caused by other environmental or genetic factors. Children who have factors that lead to good language ability enjoy hearing stories, and their caregivers adapt by reading to them more. Children without those factors react poorly to being read to, so their caregivers read to them less. A randomized controlled trial would tell us much more about whether reading actually causes any later outcomes.