In the context of migration-related disparities, a significant influence of general language competencies in the language of instruction is assumed in the subject of mathematics. Furthermore, the relevance of subject-specific language competencies and the use of language-based learning opportunities in mathematics instruction is discussed. This study analyzes the relationship between general language and mathematical competencies at the beginning and throughout the third grade, taking into account additional language-related characteristics. The results support the demands for a language-sensitive mathematics instruction that particularly focuses on subject-specific linguistic structures.