The use of data for educational decision making has never been more prevalent. However, teachers and school leaders need support in data use. Support can be provided by means of professional development in the form of "data teams". This study followed the functioning of 4 data teams over a period of 2 years, applying a qualitative case study design. The findings show that data use is not a linear process, and that teams go through different feedback loops to reach higher levels of depth of inquiry. The data team procedure is a promising way of enhancing data-based decision making in schools.