This exploratory classroom-based study examined changes in Japanese STEM undergraduates’ pragmatic awareness and production following a two-week intervention involving explicit pragmatics instruction on English suggestions. The instruction was integrated into a first-year English course incorporating project-based learning (PBL). Thirteen first-year pre-intermediate learners completed written discourse completion tasks (DCTs) before and after the instruction. Additional qualitative data were collected from a recorded peer-feedback interaction embedded in the project and from learners’ post-task reflections. The instructional sequence, adapted from Roever (2022), included noticing of model expressions, metapragmatic discussion of directness and mitigation, and guided practice leading to a semi-authentic peer feedback task. DCT scores increased from pre- to post-instruction. Qualitative analyses further revealed that learners broadened their repertoire beyond formulaic direct expressions to include conventionally indirect and mitigated forms (e.g., “How about …” and “Maybe you could …”), as well as supportive strategies such as reason-giving and collaborative repair. However, learners reported difficulty using indirect forms in real time due to limited formulaic resources and cognitive load. Overall, the findings suggest that integrating explicit pragmatics instruction into a context-rich PBL course can support learners’ production of suggestions and expand their repertoire of pragmatically appropriate forms.