Despite the popularity of the promotional activities of low external input agriculture (LEIA), systematic evaluations of the impact of these activities are scarce. This paper discusses an impact evaluation study of a training project on LEIA in Guatemala. The evaluation design is based on a simple quasi-experimental design and complemented by qualitative methods of data collection. The paper illustrates the utility of this kind of mixed-method evaluation for studying the outcome and impact of small-scale development interventions given their specific constraints of money, expertise and time. In addition, a number of specific lessons regarding the role of the evaluation study, the training project and the adoption of LEIA practices are highlighted.