This study explores how four teacher teams introduced differentiated instruction into their practice. It draws on Tomlinson's conceptualisation of differentiated instruction to respond to diversity in their classroom. The aim of this study is to document to which extent participating teachers achieved in doing so. A participatory action research design was set up. First teachers were trained to respond to heterogeneity aided by a tailor-made professional development program. Second an implementing period followed in which the participants worked collaboratively in teacher teams and were coached while implementing differentiated instruction. Field notes and interview transcripts (n = 20) with participants were collected. These were analysed thematically. Results show that teachers succeeded in implementing a range of strategies associated with differentiated instruction. In particularly they use cooperative learning strategies to accommodate heterogeneity. However, as the instructional design was not organized responsively this did not result in a practice of responsive teaching. In this study, the implementation of differentiated instruction is shown to be a complex type of educational change. We propose to conceptualize the practice of differentiated instruction as a teachers' competence with higher and lower achievement level.