The role of vocabulary components in second language learners' early reading comprehension

Background In countries with German as an official language, children with German as a second language perform overall worse in school than their German native speaking peers. This particularly affects written language skills, which require advanced language knowledge. The reasons are manifold, but one is prominent, namely poor vocabulary knowledge. Vocabulary, however, consists not only of the number of known words but also of a complex and hitherto under-researched lexico-semantic framework, which is referred to as vocabulary depth. Method In the present study, a sample of 373 children (322 German native speakers and 51 with German as a second language) was examined longitudinally in Grade 2 and 3 for their reading comprehension and vocabulary breadth and depth. Vocabulary depth was defined as relational and semantic word knowledge. Latent change score models on vocabulary breadth and depth development including reading precursor skills, non-verbal intelligence and SES were conducted. Results The children with German as a second language scored lower than the native German speakers in reading and vocabulary tests, with the difference in vocabulary depth being more pronounced than in vocabulary breadth. Importantly, the differences did not tend to diminish over time, which could have been expected. The differences in reading comprehension can be accounted for mainly by the variations in vocabulary, especially in vocabulary depth. Conclusions These findings emphasise the importance of including not only vocabulary breadth but also vocabulary depth in the context of reading research on children who do not speak the majority language.