This article presents a comparative study of German and Swedish teachers' continuing professional development (CPD) in relation to student assessment. It investigates the sources teachers use to improve their knowledge about assessment and the relationship this has to different national contexts. Assessment, as well as evaluation, defines what counts as valid knowledge and how this can be measured. As such, assessment is a major focus of teaching and specifies constraints and possibilities for teacher practice in the classroom. Teachers are seen as agents in a regulated CPD marketplace, and within this framework teachers make decisions about the knowledge sources they use to educate themselves about assessment. These choices can be seen as expressions of what they perceive as important and relevant in relation to assessment. We argue that this expression of opinion can contribute to an understanding of teachers' professional autonomy, especially in relation to their decisions about a crucial aspect of their profession. In this way, we propose a way to conceptualize the impact of the national context on teachers' CPD. (Contains 6 tables.)