Raising the incomes of agricultural households is central to reducing poverty in Uganda. In many areas of the country agriculture has encroached into marginal or fragile lands, leaving little room for the expansion of agricultural lands (Kraybill, Bashaasha, and Betz 2009). Additionally, soil degradation has become a barrier to agricultural productivity (Pender et al. 2004), especially in the Eastern region of the country. Farmers now look for alternatives that will increase output without further depleting soil fertility or expanding into fragile lands. Agricultural extension is the primary government mechanism through which developing country governments attempt to improve the knowledge and methods that farmers use to increase output; However, many extension programs throughout Sub-Saharan Africa have the reputation of being largely ineffective (Dejene 1989; Gautam 2000). This study estimates an agricultural production function for 3 farm sizes to determine whether agricultural extension has differential effects on farms of different size. Extension is found to have a positive and significant relationship with the value of output produced for small and large farms, but has not significant relationship with the value of output for medium size farms. This result has distinct policy implications for the design and implementation of agricultural extension programs in Uganda and other parts of Sub-Saharan Africa.