The present study investigates the productivity effects of agricultural extension services in Uganda drawing upon Uganda Agriculture Census (UCA) data (2008/2009). The descriptive show that 21% of farming households had accessed extension services from public and other providers. The proportion of household who initiated contact extension were only 3% compared to 8% through predetermined visits by extension agents and 10% through both routine and on demand. However, it was revealed that popular information sources among farmers were radio (88%) and fellow farmers (72%). We estimated treatment effect of extension contact using counterfactual framework. Results of the treatment effect model show a significant effect of access to extension services on yield. On average, farming households who had extension contact were more productive than farming households with no extension contact Implementing the ivtreatreg stata command that take care of the selection into homogeneous and heterogeneous treatment, we estimated the average treatment effect (ATE), average treatment effects on the treated (ATET) and average treatment effects on the non-treated (ATENT). The ATE had a negative sign meaning that farming households who had extension contact would have been less productive if they had not got access to extension services. The negative average value of ATET (x) implies that farming households who had extension contact would on average produce less than one tonne per acreage if they get more access to extension services, demonstrating diminishing returns associated with more and more extension contacts. The mean value of the ATENT(x) predict that on average farming households who had no extension contact would have been more productive if they had extension access. Crop productivity OLS and 2SLS estimates show that extension contact matters for farmer productivity more so if extension contact is initiated by farmer. The study recommends that extension contact has favouarble effect on farmer productivity and therefore efforts should be geared at reforming the extension system to reach the majority of unreached farmers and focus more on empowering farmers to demand extension services themselves.