In the language assessment literature, grammatical ability is widely accepted as a key component of second language (L2) ability in general and L2 writing ability in particular. Indicators of grammatical ability have been investigated in L2 writing research, but the indicators L2 writing teachers attend to when determining grammatical ability levels of their students have not been studied. Furthermore, there is no research on what students know about their teachers’ assessment criteria and how that knowledge might affect their writing and learning process. This mixed methods triangulation study examines these questions in university L2 academic writing classes through a quantitative text-based analysis of academic essay exams, student questionnaires, and teacher and student interviews. The combined results of all data sources indicate that the teachers in this study focus primarily on accuracy when assessing grammatical ability. This leads to risk avoidance behaviour by students and may have a negative impact on their learning as students adapt their writing to meet above all their teachers’ expectations for grammatical accuracy.