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.
