The education and professional development of foreign Language teachers is a challenging endeavour - for the (student) teachers themselves as well as the teacher educators involved. This study investigates a cohort of 12 English teachers enrolled in the M.A. programme 'E-LINGO - Teaching English to Young Learners' in a qualitative-interpretative study. The aim is to explore if, how and under what circumstances classroom action research, a core component of the programme, can foster teacher learning. Since the participants have different educational and cultural backgrounds and various levels of professional experience in the field of Language teaching, they offer different perspectives on the object of research. Data from multiple sources (semi-structured group interviews, learning logs, portfolios and observation notes) were triangulated and interpreted to elicit indicators for learning and development in the form of critical learning incidents. The results suggest that not only cognitive, but also social and affective factors constitute the complex process of teacher learning.