We combine panel survey data with a randomized controlled trial conducted among 250 villages in Malawi to test the effectiveness of a standard agricultural extension service. The two main tools of the service are a mid-season farmer field day and farmer club managed demonstration plots. We find that farmers in villages who were invited to attend the farmer field days display an increased knowledge of Integrated Soil Fertility Management Practices and a higher probability of adoption (plans), with the majority of the effects concentrated among non-attendees. However, when combined with in-village demonstration plots, farmers who participate in the demonstration plots display a higher knowledge of what we refer to as “detailed” production knowledge, such as types of inputs, quantity of inputs, and increased likelihood of planning to adopt these.