This study was conducted in a large-scale environmental literacy project. In the project, we developed a Learning Progression Framework (LPF) for matter and energy in social-ecological systems; the LPF contains four achievement levels. Based on the LPF, we designed a Plant Unit to help Levels 2 and 3 students advance to Level 4 of the LPF. In the present study, 12 teachers used the Plant Unit to teach, and their students took an LPF-based assessment both before and after the teaching intervention. We observed and videotaped 20 lessons from four of those participating teachers. In this article, we report on how teachers' teaching practice and students' learning practice in classrooms mediate the intervention's impact on students' learning outcomes. Regarding teaching practice, we focused on how teachers used discourse strategies to engage students in meaningful learning. Regarding students' learning practice, we studied epistemological frames that the students used to guide their thinking. The results show that encouraging students to talk about the "how" and "why" behind their answers did not always lead to students' use of productive frames and positive learning gains. We found that one teacher, Ms. S, successfully fostered students' use of productive frames by using discourse strategies that target the specialized ways of reasoning behind the science content and the rationale for scientific investigations. Ms. S' students also achieved a learning gain higher than the average learning gain in the intervention. These results suggest that discourse strategies aligned with the LPF play an important role in learning progression-based interventions.