Taking the perspective of a language program director (LPD), this practitioner research (PR) study describes how analysis of learners' reflections written for an advanced undergraduate German course in the United States helped an LPD see how students had experienced learning grammar in lower-level instruction. The study analyses a semester-long project based on the PR framework of exploratory practice (EP), in which students (n = 30) pursued individual questions ('puzzles') about German grammar that would be most meaningful to them in their language learning journey. Initial analysis of the students' questions revealed a general preference among learners to investigate grammar topics previously covered in the lower-division curriculum. In-depth case studies, focused on two learners' experiences with EP, show how the project allowed students to investigate their grammar puzzles using resources across the entire curriculum, including dialoguing with teachers and students in other courses. The study looks to threshold concept theory to theorize students' learning experiences vis-à-vis L2 grammar (specifically inflectional morphology, i.e. case markings) and argues that the flexibility of the EP framework and its core tenets of working towards understanding and involving others supported the LPD in seeing how learners understood and felt about German grammar and grammar instruction across the larger curriculum.