Though Germany has long provided education for children speaking a heritage language and received two recent waves of refugees, reliable assessment tools for diagnosis of language impairment or the progress in the acquisition of German as a second language (L2) by refugee children are still lacking. The few tools expressly targeting bilingual populations are normed for younger, early successive bilingual children. This study investigates 27 typically developing children with Arabic as first language (L1), comparing 15 school-age Syrian refugees (6;6–12;8), with 12 heritage speakers (6;0–12;9). We assess the L1 and L2 skills of these two groups with standardized tests, but crucially with an Arabic and a German sentence repetition (SRT) as well as a nonword (NWRT) repetition task (Grimm & Hübner, in press; Marinis & Armon-Lotem, 2015). Comparable scores emerged only for German LITMUS-NWRT and Arabic LITMUS-SRT. Refugee children had an advantage in L1 measures, for example, vocabulary and morphosyntactic production, whereas they performed poorly in the German LITMUS-SRT and other L2 tests involving morphosyntax and vocabulary even with 24 months of systematic exposure. This indicates that the acquisition of adequate vocabulary and complex syntax takes time. The paper explores factors influencing performance on the repetition tasks and relates the results to established diagnostic procedures and educational policies.