Icelandic children’s vocabulary between ages 4 and 8: Longitudinal study of growth-rate and stability

Abstract

Multiple studies of children learning English have confirmed the amazing speed of children’s vocabulary growth in the preschool and primary school years as well as its vital importance for children’s future literacy development and learning. Already at this early age, however, important individual differences in vocabulary size are consistently reported and they tend to increase rather than decrease with age. Until recently, research on Icelandic children’s language development has been rather sparse and fragmentary, hampered among other things by the lack of assessment tools. The longitudinal project reported on in this paper, Development in early childhood: language development, literacy, and self-regulation, is the first of its kind in Iceland. The overall goal of the project was to develop necessary assessment tools and provide up to date scientific evidence of Icelandic children’s language (vocabulary, morphology, listening comprehension and spoken and written text construction) and literacy (phonological awareness, letter knowledge, word reading, spelling, reading comprehension) development between ages 4 and 8 and investigate their mutual interactions. Furthermore, we wanted to explore the range of individual differences at this age and how they were related to various background variables, social-cognitive skills and to the children’s later literacy development. In the present paper the focus is on one aspect of the study: The growth-rate of Icelandic children’s vocabulary from age 4 to 8, as measured by a test of receptive vocabulary developed for this project, Isl-PPVT.The study employed a sequential design, including two groups of monolingual Icelandic children that overlapped in first grade (age 6). The younger group included 111 4-year-old children (Mean age = 4;6, SD = 0;3) from eight preschools in Reykjavík, 56 girls and 55 boys, and the older 111 6-year-olds (M = 6;6, SD = 6;3) in 1st grade, including 65 boys and 46 girls. All children were followed up for three years and the younger group was tested again at ages 7 and 8. The children were tested individually in their respective schools during spring term each year. Finally, reading comprehension scores from the standardized 4th grade national test were collected for all children. In addition to descriptive statistics, the effects of age and gender were investigated using multilevel growth models followed up with F-tests for the significance of the effects observed. The stability of the Isl-PPVT was assessed using Spearman’s rank-order correlation between each child’s successive data points, and its validity by calculating Pearson’s correlation coefficient between the children’s score on the Isl-PPVT and their scores on another vocabulary test (definitions) as well as on tests of morphology and listening comprehension, and, finally, with reading comprehension in 4th grade. Consistent with studies of English-speaking children, the results show that the Icelandic children’s vocabulary grew significantly between ages 4 and 8. Neither the difference between girls and boys nor that between the 6-year-olds in the younger and the older group were significant according to unpaired t-tests, allowing us to merge the groups into one (covering all ages between 4 and 8) for some of the analyses. Significant concurrent and predictive correlations were observed between children’s scores on the new vocabulary test over the five-year period, thus supporting its stability and validity. Its validity was further confirmed by significant correlations with the other vocabulary measure, as well as with two other language measures (morphology knowledge and listening comprehension) and with reading comprehension in 4th grade. However, due to ceiling effects in the last two waves, new items need to be added to the more difficult section of the Isl-PPVT in order for the test to distinguish equally well between the strongest and the weakest children over the entire age-range from 4 to 8. In view of the far-reaching implications of vocabulary for later reading comprehension and for children’s learning and development in general, the results underline the importance of early identification and appropriate measures/intervention for Icelandic children at risk, no later than at age 4.