This paper investigates how language awareness influences the writing abilities of bilingual heritage language speakers. The study includes 175 bilingual 9th and 10th graders with Italian, Greek, or Turkish as their L1 and German as an early L2. The analysis is based on a corpus of narrative and argumentative texts in L1 and L2 and a language awareness test to explore semantic, pragmatic, and textual knowledge that was administered in both languages. We found that the students’ writing abilities in both languages were highly interdependent and there was a significant correlation between achieving high scores in the heritage language test and achieving equally high (or even higher) scores in the L2 test. The results further point to a significant correlation between metalinguistic awareness and writing abilities. However, there was a higher correlation between metalinguistic awareness and text level scores in the heritage language, which shows that writing abilities in this language are more dependent on metalinguistic awareness than in the language of schooling. Moreover, differences were found between the respective language groups and different school types. Based on these results, it is argued that the fostering of language awareness ought to be implemented more intensively in the language classroom.