Though extension services have long since proved their value to agricultural production and farmer prosperity, their record in sub-Saharan Africa has been mixed. To study the impact of such programs on farmers' learning about agricultural technologies, we implemented a quasi-randomized controlled trial and collected detailed panel data among Malawian farmers. Based on those findings, we develop a two-stage learning framework, in which farmers formulate yield expectations before deciding on how much effort to invest in learning about these processes.