Evaluation is a necessary component of plant health programs designed for and implemented in research, extension, and international development settings. Outcome Mapping is a method of program planning, observation, and assessment in which changes in behavior, relationships, or actions of the target groups (boundary partners) are evaluated during program implementation. Outcome Mapping was used to evaluate stakeholder participation in participatory variety selection trials for tomato and soil health training for tomato farmers in Tanzania. Boundary partner participation varied between the three villages evaluated and predicted adoption of new varieties assessed one year later. Outcome Mapping was valuable in tracking progress during program implementation and can indicate long-term impacts of the program. Accepted for publication 21 November 2016.