Although perceptual explanations for reading problems were common in the early discussions of Learning Disabilities, educators now mostly agree that the language factors have far greater influence on reading problems. A recent study by Nicole Halaar and colleagues underscores this idea and, especially importantly, points to the importance of early childhood language development in later reading competence. In fact, although genetic factors play a role in later reading competence, environmental exert substantial influence.
Of course, given the extensive work on them over the past 20 years, educators understand the importance of phonemic awareness and decoding in reading. But these factors do not completely explain the variation in outcomes for children learning to read. The contributions of semantic and syntactic factors must be included to move closer to explaining why children differ in their reading outcomes, especially when the outcome of concern is facility in comprehending what one has read.
To understand the contributions of vocabulary and grammatical skills to reading comprehension, it would be beneficial to understand the roles that genetic and environmental factors play in language ability and reading competence. Halaar and colleagues waded into this problem by examining relationships between the pre-school language ability of twins from the United Kingdom and their later primary and elementary grade reading competence.
Purpose: Language acquisition is predictive of successful reading development, but the nature of this link is poorly understood.
Method: A sample of 7,179 twin pairs was assessed on parent-report measures of syntax and vocabulary at ages 2, 3, and 4 years and on teacher assessments of reading achievement (RA) at ages 7, 9, and 10 years. These measures were used to construct latent factors of early language ability (LA) and RA in structural equation model-fitting analyses.
Results: The phenotypic correlation between LA and RA (r = .40) was primarily due to shared environmental influences that contribute to familial resemblance. These environmental influences on LA and RA overlapped substantially (rc = .62). Genetic influences made a significant but smaller contribution to the phenotypic correlation between LA and RA, and showed moderate overlap (rA = .36). There was also evidence for a direct causal influence of LA on RA.
Conclusions: The association between early language and later reading is underpinned by common environmental and genetic influences. The effects of some risk factors on RA may be mediated by language. The results provide a foundation for more fine-grained studies that examine links between specific measures of language, reading, genes, and environments.
Halaar and collegues found that nearly 60% of the relationship between early language ability and later reading ability was a result of shared environmental factors. That is, much of the environment of children that affects that competence in the syntactic-semantic realm also affects their reading competence. They conclude that the reasons children who have better language skills also have better reading outcomes are that (a) the same environmental factors influence both language and reading, (b) the family environment influences both, and (c) the family environment influences performance at both the pre-school and school ages.
Before anyone leaps to the conclusion that these results show that environment trumps heredity, however, it is important to note that the researchers also found that genetic factors accounted for about one third of the relationship between early language and later reading. As is usually the case in studies of the contributions of genetic and environmental factors, this is not a case of either-or, but of both-and.
Halaar, N., Haylou-Thomas, M. E., Dale, P. S., & Plomin, R. (2008). Why do preschool language abilities correlate with later reading? A twin study. Journal of Speech, Language, and Hearing Research, 51, 688-705.