Autonomy-supportive teachers energize students' agency and initiative. However, few studies consider whether agentically engaged students energize more autonomy-supporting teachers. We asked 2,908 middle and high school students in physical education courses to report their agentic engagement and the autonomy supportiveness of their teachers. Data were collected at four time points over one academic year. We tested two reciprocal effects models relating student perceptions of autonomy-supportive teaching and their agentic engagement: a between-person cross-lag-panel model (CLPM) and a within-person CLPM with random intercept. Both models supported the bidirectional reciprocal relations between perceived autonomy-supportive teaching and agentic engagement. Based on student perceptions, prior agentic engagement led to increased autonomy-supportive teaching and prior autonomy-supportive teaching led to greater agentic engagement. We discuss the practical implications of these findings for classroom research and recommend teachers to inform students early in the school year that they will welcome students' input and initiatives.