Introduction Previous research has mainly studied the impact of activity explanation on performances (e.g., Chi, 2009), but little research has been done to examine its impact on the development of a competence. Objective A model of dynamic analysis of competence (Coulet, 2011) has been used to measure the impact of activity explanation on the development of a technical competence. Method Explanation of tasks of varying complexity has been manipulated in two experimental studies; effects of activity explanation have been measured on objective performance, perceptions related to the task and final explanations. Results Participants who explained their activity not only performed better on the tasks, but also showed more positive perceptions of their relations to the task and a better ability to produce didactic explanations. Conclusion Psychological processes involved in explaining activity and their implications are examined and discussed.