This dissertation presents a study of teachers' agency in assessment practices. In recent decades, assessment has become an increasingly prominent aspect of teachers' work. Governance ambitions through more explicit regulation and pedagogical trends informed by research on formative assessment, have aimed to enhance the quality of learning while promoting greater equity in teachers’ assessment practices. However, research shows that teachers differ in both how assessments are conducted and in what is being assessed. The research problem in this dissertation is therefore grounded in the question of how and why teachers’ assessment practices vary. The aim of the study is to describe and analyze teachers’ agency in assessment practices in grade six, which is accomplished through four case studies where the empirical collection consisted of observations and interviews. Teachers' experiences, attitudes, and approaches to the cross-pressure of expectations and conditions surrounding their pedagogical work are understood theoretically through an ecological perspective on agency. The findings demonstrate that teachers' assessment practices differ in terms of the dimensions of assessments, namely, the purposes of assessment, its use, and its relationship to teaching. The dissertation further shows that teachers’ approaches to the interaction between individual characteristics and structural and classroom conditions, analyzed as rationales for assessment, can help explain why and how assessment practices vary, as different rationales highlight different dimensions of assessment in varying ways.

The dissertation argues that agency in assessment practices can be understood within the tension between teachers’ educational ideals and the regulations outlined in governing documents. In the tension between educational ideals and regulations, aspects related to the classroom context may become significant. These classroom-contextual aspects also differ in nature from more structural factors, in that teachers can exert influence over them. This tension is primarily expressed across four domains: learning objectives, student participation, fairness and reliability, and consequences of assessment. The variation in assessment practice, for instance, in how research findings on formative assessment are implemented, or how efforts to standardize teachers’ assessment work through policies and reform packages are realized in practice, is therefore proposed to be understood through the lens of teachers’ agency within the tension between educational ideals and policy directives.