Maker spaces are generally regarded as a valuable innovation in comparison to traditional education, although it is largely unclear what is exactly learned. This deficiency hampers the deployment of maker spaces, particularly their embedding and integration in the existing practice in formal education. In the work presented here, we explore the possibility of having learners self-report on their learning experience. For this purpose, we developed an easy-to-use visual tool for assessing learning of 21st Century Skills in children’s maker space activities, the Self-Evaluation Tool (SET). Particularly, we investigated the validation of the SET for the self-evaluation of learning activities in the maker space and how children evaluate their own performance in the various domains. The results show higher scores on learning goals in subjectification and lower scores for socialization. Future research will focus on a comparison of the different types of maker programs.