Vocabulary trajectories in German-speaking children from 18 months to three years: a growth mixture model

Children acquire vocabulary at different growth rates. The aim of this study was to identify subgroups of different vocabulary trajectories in a community sample of L1 German-speaking children aged 1;6 to 3;0 to enlarge the understanding of vocabulary trajectories. Parents filled out vocabulary checklists at four measurement times, each six months apart. Growth mixture modelling was used to naturally determine latent classes of observed vocabulary growth curve patterns. Six distinct trajectories of vocabulary growth were identified and characterised. Children's (<i>N</i>=198) vocabulary abilities were divided into the following subgroups: "far above average" (2.0%), "above average" (6.6%), "typical" (70.2%), "below average" (14.1%), "early below average" but caught up with their peers over time (5.6%), and "far below average" (1.5%). Socioeconomic status differed significantly between subgroups.