Written error corrections are an integral part of foreign language instruction. They are intended to encourage foreign language learners to reflect on their mistakes and their causes, thereby revising erroneous learning hypotheses about the target language. Although relevant didactic literature attributes this potential particularly to indirect corrections with correction symbols, there are hardly any empirical studies on the topic in the field of German as a foreign and second language (DaF/DaZ). Based on this research gap, the present study investigates the potential of written grammar corrections to promote language acquisition among DaF learners at an intermediate level. Drawing on the results of a detailed writing process analysis, the study demonstrates through case studies which factors influence the effectiveness of error corrections.