Formative peer and self-assessment play an important role in supporting student learning, but can be challenging to implement in the classroom due to teachers' limited assessment literacy. This study examined the effects of a professional development program designed to enhance assessment literacy among primary mathematics teachers. The program also addressed teachers’ epistemological beliefs. In a randomized pretest–posttest design with a wait-list control group, 102 teachers participated. Assessment literacy was examined using video-based and text-based vignettes, while epistemological beliefs were measured using Likert-scale items. Teachers who attended the program demonstrated higher performance in specific aspects of assessment literacy, particularly in declarative knowledge about the purposes and benefits of peer and self-assessment, as measured by the text vignette. Results from the video vignette, however, did not reveal transfer effects to authentic classroom settings. Transmissive beliefs remained stable, whereas constructive beliefs were positively associated with improvements in assessment literacy.

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