Data use is increasingly considered to be important for school improvement. One promising strategy for implementing data use in schools is the data team intervention. Data teams consist of teachers and members of the school leadership team, who collaboratively analyze and use data to solve an education-related problem at the school. This mixed-methods study aims at measuring the effects of working in a data team on the application of data use in ten secondary schools by using questionnaires and case study interviews. The results show that at the end of the intervention period, educators on the data teams did not apply data use more often for accountability actions, but seemed to be more aware of data use for school development and instruction. Furthermore, it seemed that the teachers made a start at applying data use for instructional actions.