You don’t have to be a linguist or reading specialist to suspect that language necessarily precedes reading. So it’s probably no surprise that research shows that children who are late talkers are more likely to have reading problems when they enter school.

What is less clear is the nature of the association between early language problems and later reading difficulties. Is it simply that the genes that predispose a children to have trouble with language also predispose them to have trouble with reading?

Or is something present or lacking in children’s environments at the root of the later reading problems?

A research team of English and American researchers, led by Nicole Harlaar at the Institute of Psychiatry in the UK have been investigating these issues. They examined data collected from parents of 7,179 twin pairs in England and Wales on their language abilities at ages two, three, and four years and data from their teachers on their reading abilities at ages seven, nine, and ten.

Twin research is a common way to tease apart the influences of genes and environment. If something in the twins’ environment accounts for their language or reading abilities, then identical twins (who are genetic duplicates of one another) should be no more similar than fraternal twins (who share, on average, only 50 percent of their genes). If genes are more important, however, then identical twins would be more similar than fraternal ones.

They found the children’s home environments, more so than their genetic make-up, accounted for both language and reading abilities, but that both genes and environment were important.

The evidence also suggests that having a broader vocabulary and understanding of language structure early in life fosters later reading skills. In other words, it’s not enough to be able to sound out words phonetically, one must understand the meaning of words and sentences to really read.

These findings suggest that changing something in children’s home environments could accelerate first language and then reading. But it’s not clear what that something might be. Moreover, children who are genetically vulnerable to language and reading problems would probably continue to have difficulties despite the change at home. For these children Harlaar and her colleagues say, “other types of support will be necessary”, although they offer no suggestions about the nature of this support.

Summary of ‘Why Do Preschool Language Abilities Correlate With Later Reading? A Twin Study” by Nicole Harlaar, Marianna E. Hayiou-Thomas, Philip S. Dale, and Robert Plomin in Journal of Speech, Language, and Hearing Research, June 2008, Volume 51, Issue 3, pp. 688-705.