The need for increased monitoring and evaluation within the conservation sector has been well documented, and includes the monitoring and evaluation of training activities. We evaluated the impacts of a long-term training programme in Mauritius, using a questionnaire and semi-structured key informant interviews to develop a theory of change from the perspective of the trainers, and validated it against participants' perceptions of the benefits of training. Our findings indicated that an important outcome of training was to increase participants' belief that they could effect change, also called perception of control; this is related to an increase in a trainee's practical skills, which enables them to become more effective in their work. However, if a trainee's work environment was negative, the impact of training on practical skills, job performance and perception of control was lower. Neither the acquisition of conservation theory nor the opportunity to network was perceived by participants as improving their conservation performance, despite trainers anticipating that these matters would be important. Perception of control and work environment should therefore be considered when designing conservation training programmes, and the effectiveness of teaching conservation theory and networking should be examined further.