Over the last decade, many countries have implemented assessment systems meant as tools for school improvement. This article examines how school leaders in Norway respond to the expectations of national authorities regarding the use of assessment results to transform practice. The research draws on data from a survey study investigating how school principals use national tests, results from student exams and the Pupil Survey to improve learning in schools. We suggest that the framework of 'expansive learning' represents a novel perspective designed to change approaches by focusing on how change processes in schools need to acknowledge critical investigations and tensions. The findings show that, while school leaders initiate discussions of the assessment results, many of these discussions do not lead to new practices in the classroom, mainly because the school leaders perceive teacher resistance. This study contributes to the research field by acknowledging the challenge of using assessment to improve practice within the school.