The purpose of the present doctoral thesis was to investigate the contributions of word knowledge to the development of reading comprehension and word recognition abilities. The thesis is comprised of three empirical studies:
The aim of the first study, a meta-analysis, was twofold: (a) to provide the best possible estimate of the contribution of early vocabulary knowledge to later reading comprehension, and (b) to investigate possible contributions from early vocabulary to later word recognition abilities. The results of the analyses revealed a moderate relationship between vocabulary and reading comprehension, whereas the average correlation between vocabulary and word recognition abilities was somewhat smaller. Taken together, the results demonstrate that vocabulary is a robust predictor of reading comprehension, a finding that may be taken as support for teaching vocabulary in preschool and school.
The goal of the second study was to investigate the development of word knowledge by exploring the relationship between lexical and grammatical growth. Annual assessments of grammatical and lexical knowledge were conducted in a cohort of pre-school children over the course of two years, and the data from these assessments were analyzed using latent change score models. The results of the analyses supported a model depicting bidirectional effects between lexical and grammatical growth, indicating that there is a dynamic relationship between the two constructs.
The purpose of the third study was to explore the hypothesis that teaching children knowledge of word forms and meanings supports the development of reading comprehension. This hypothesis was examined by investigating the effects of a comprehensive word knowledge intervention on the language and literacy skills of poor readers. At the end of the study, statistically significant effects of the intervention were identified on several measures of language and a measure of reading comprehension. The results indicate that comprehensive word knowledge instruction is effective in improving reading comprehension abilities.