Russian and Turkish are the most frequently spoken and intensively investigated heritage languages in Germany, but contrastive research on their development in early childhood is still missing. This longitudinal study compares the trajectories of expressive lexicon development in Russian (n = 70) and Turkish (n = 79) heritage speakers and identifies predictors for their lexicon size at preschool age. Heritage lexicon size was tested with two comparable tests assessing the expressive lexicon at four test points between the mean ages of 3.3 (range: 25–49 months) and 5.6 (range: 54–78 months) years. The influence of language-related factors, such as input quantity, parents’ heritage language proficiency and age of onset (AoO) of German, and other potential predictors, i.e., intelligence and socio-economic status, is evaluated. Results show that the Turkish group’s abilities grow slower but are similar at the last test point. Common predictors for lexicon size are input quantity from siblings and AoO. Group-specific influences are parental input quantity in the Russian group and siblings’ proficiency in the Turkish group. Our findings emphasize the interplay of input quantity and society language AoO for heritage lexicon development. The relevance of our results for the usage-based theory of language acquisition is discussed.

Research question: How does Russian and German reading comprehension develop during the first 3 years of primary school in Russian heritage speakers and which factors predict performance in each language? Methodology: 40 Russian-German children were tested annually from first to third grade (age in grade 1 M = 7; 1 years). Reading was assessed with comparable Russian and German word and sentence reading comprehension tests. The Russian test was available in Cyrillic and Latin script (the latter for children who could not read Cyrillic letters). Potential predictors included lexicon size in Russian and German and rapid automatized naming (RAN) of numbers (both assessed in primary school). Other factors were assessed in kindergarten, that is, nonverbal reasoning and, derived from a parents’ questionnaire, their socioeconomic status and language input in the family. Data and analysis: Linear regressions were used to compare the development of Russian and German. Stepwise regression analyses identified predictors for reading comprehension in each language. Findings: German reading ability improved faster than that of Russian, likely due to the increasing amount of German input outside the family, literacy instruction in German at school, and the large variance in Russian literacy abilities. Children who could read Cyrillic script, who likely received some form of Russian literacy instruction, and who had a larger Russian lexicon size exhibited better reading performance. These results are discussed regarding the divergent attainment trajectories. Decisive factors for German were German lexicon size and RAN. Originality: This longitudinal study tracked Russian and German reading development over 3 years in primary school, assessed Russian reading in Cyrillic and Latin scripts, and identified predictors for bilingual reading development in both languages. Implications: To become proficient readers in their heritage language, children need to have a substantial lexicon size and receive literacy instruction.

Erwerbsprofile des Deutschen im mehrsprachigen Kontext was published in Deutsch in Europa on page 75.