The use of machine translation (MT) tools remains controversial among language instructors, with limited integration into classroom practices. While much of the existing research into MT and language education has explored instructor perceptions, less is known about how students actually use MT or how student use compares to instructor beliefs and expectations. In response to this gap, the current article explores how students use MT while writing and how this use compares to instructor perceptions via two studies: a computer-tracking study of how 49 second semester-level language learners (French, Spanish) use MT and a qualitative survey of 165 US-based second language educators' beliefs about MT. Findings highlight important areas of alignment (e.g., MT input at word level) and divergence (e.g., MT output analysis strategies) between student use and instructor perceptions as well as layered tensions in what mediates student use of MT tools. The article concludes with calls for more research on student use and an outline for how to approach MT tools in language education in ways that support existing student practices.