The alignment of teaching and assessment in chemistry courses is critical for the practice of science and positive student learning outcomes. This paper addresses how instructors can align what they do in class with assessments across topics to improve students' understanding and explanations of chemical phenomena. We drew on the foundations of Phenomenon-Based Learning to introduce how observable events can be used as an entry point into causal mechanistic reasoning, an essential explanatory practice for scientists. This cross-institutional study focuses on two chemical phenomena: dissolution and boiling point. Students from three different learning environments completed phenomenon-based tasks centered on these two phenomena, and their responses were analyzed for different levels of causal mechanistic reasoning. We then analyzed instructors' dialogue for evidence of causal mechanistic reasoning from content units where these phenomena were emphasized. Using students' responses to the tasks and the instructor dialogue from the content units, we observed students activating more resources related to particulate behaviors when explaining the focal phenomena after instruction emphasized using causal mechanistic reasoning to explain phenomena. This is noteworthy, as it highlights the promise of sustained phenomenon-driven curricula by helping students explain events using deeper levels of reasoning. Our work provides evidence for instructional and curriculum developers to design courses in a way where we are demonstrating to students what practicing scientists do. We discuss implications for practitioners that include ways to use observable events and chemical phenomena as a foundation to promote causal mechanistic reasoning in chemistry.