This study carries out the impact evaluation of Farmer Field School (FFS) training program on the technical efficiency of smallholder farmers. The FFS program was sponsored by the Ethiopian government and launched in 2010 to scale-up best agricultural practices in the country. The study aims to compare changes in the technical efficiency of those FFS graduate and non-FFS graduate maize producing farmers in Ethiopia, Oromia. For this, panel data were collected in two rounds from 446 randomly selected households from three districts consisting of 218 FFS graduate farmers and 228 non-FFS graduate farmers. The analytical procedure has involved three stages: in the first stage, descriptive analyses were used to detect existence of the difference in the outcome indicators between the two farmer groups. In the second stage, we have applied a semi-parametric impact evaluation method of propensity score matching with several matching algorithms to estimate the program impact. In the third stage, we used Difference-in-Difference as robustness check in detecting causality between program intervention and the technical efficiency. The combined uses of these alternative estimation techniques indicate that the program has a negative impact on the technical efficiency of the FFS graduates. Numerous plausible explanations for this outcome are discussed, and recommendations for improvements are suggested accordingly.