We evaluate a technology upgrading intervention for smallholder dairy farmers in Uganda, showing that a simple version of the “contact farmer” extension model can meaningfully increase farmers’ revenues. In a program that provides no monetary incentives to local farmer trainers, backstopping by professional extension agent and advertising prosocial motivation reinforce impacts. We find no statistical evidence that program effects vary by farmers’ characteristics. Being exposed to a broad menu of 33 different feeding practices, farmer trainers re-adjust feeding practices to fit their labor and capital endowments; this selection according to comparative advantage may explain the program’s widespread and homogeneous benefits.