While a growing body of research has addressed the outcomes of K-12 foreign language (FL) study, relatively little is known about the relationship between teachers' practices and students' proficiency development (Hlas & Hlas, [Hlas, A. C., 2012]; Tschirner & Malone, [Tschirner, E., 2012]). To fill this gap, the current study, set in a large urban school district, investigates how differences in teachers' (N = 26) self-reported use of the target language (TL) and explicit grammar instruction relate to secondary FL students' (N = 2,179) yearlong gains on a standardized language performance assessment. Findings reveal a largely positive effect for TL usage, which was most pronounced in the beginner levels. Meanwhile, explicit grammar instruction yielded mixed results, beginning with a negative effect in Level I and transitioning toward a positive effect by Level IV. Collectively, the findings suggest that best practices for FL teaching may in fact vary according to the level of instruction.