The impact of formative assessment on student achievement: A study of the effects of changes to classroom practice after a comprehensive professional development programme

~22 Year-4 teachers and their classes in one Swedish municipality

Swedish Year 4 (age ~10) mathematics classrooms in a single municipality.

Teachers randomised to a comprehensive formative-assessment professional-development programme or to business as usual. Graded C rather than B: small teacher-level cluster sample in one town, and the achievement outcome was a municipality-designed mathematics test aligned to the local curriculum rather than an independent standardized measure.

The most-cited positive formative-assessment trial: a comprehensive teacher PD programme produced d ~ 0.30 in Year 4 mathematics. The effect is measured on a non-independent, locally designed test in a single municipality, which is exactly the condition under which effects inflate roughly 2x.

Randomised at teacher level, so genes cannot differ systematically between arms; the threat here is measurement alignment, not heredity.

Directly re-tested by the same developer under randomization in Bostrom & Palm 2023, which found d = 0.00. Treat this estimate as the aligned-measure efficacy upper bound.