This study investigates whether a co-designed program of unified formative assessment strategies affects pupil academic achievement. After controlling for pre-intervention gain, and school-specific pupil population complexity, the pupils of teachers that participated in the formative assessment co-design did not significantly outperform the pupils in the control group. The multilevel analysis also revealed non-significant effects of the interaction between the formative assessment intervention and performance levels on mathematical gain. This study provides valuable insights in the challenges that lie in both implementing (effective)formative assessment practices and investigating the effectiveness of a te acher community co-designed formative assessment practices program on pupil academic results.

Embedding formative assessment into everyday pedagogical practice is a complex matter for teachers. In this study, we used teacher-researcher co-design to investigate how a one-year collaboration between seven elementary school teachers and three researchers supports the design- and implementation process of formative assessment in each of the teachers’ classrooms. Our findings indicate that teacher-researcher co-design supports the implementation of a unified approach to formative assessment through teachers’ evolving conceptions. The co-design facilitated open dialogue, ongoing exchange of ideas between participants, led to a shared understanding in a teacher community and improved the teachers’ sense of ownership.