This presentation focuses on the research perspective and methodology of two studies, conducted in the Netherlands, which were aimed at describing how experienced secondary school teachers learn at work in an informal learning context. Informal learning is conceptualized as taking place in a work context characterized by a lack of systematic support for learning. Learning is understood as: undertaking activities that lead to a change in cognition and/or behaviour. The purpose of the first study was to explore how experienced teachers learn through the activities they undertake when teaching. Four teachers participated in this study that involved both observational and interview data over the period of a year. Our second study was aimed at studying the relation between teachers’ activities and learning outcomes, i.e. changes in cognition and/or teaching behavior, as they occurred over the course of a year. The presentation focuses on the research methods: specifically instruments and data analysis.