Citizen science is an expanding field in public education and learning and can bridge the gap between science and society. This benefits not only just citizen learning and scientific research, but also earlier learning in formal science education. Citizen science can foster an understanding of engagement with science as well as the perception of the relevance of scientific topics. Based on a review of several citizen science projects in school contexts, potential learning outcomes are identified, showing that citizen science can enhance aspects including pupils' motivation, interest and knowledge as well as their scientific and communication skills. Project designs with a high level of pupil involvement are found to be particularly promising in terms of achieving learning objectives. However, curricular standards require the thorough preparation of citizen science projects to enable the development of their full potential for all participants.