Despite the general consensus on the positive impact of formative assessment on student learning, researchers have not shown the underlying mechanisms between specific formative assessment strategies and academic performance on an international sample. This study examines the link between student and teacher reports of teachers' formative assessment strategies (i.e. clarifying goals and monitoring progress, providing feedback, and instructional adjustments) and students' reading achievement, based on data from 151,969 fifteen-year-olds in 5,225 schools in 19 countries/regions in PISA 2018 via multilevel analysis of plausible values. The results show that clarifying goals and monitoring progress, and instruction adjustments are positively linked to reading achievement, but providing feedback alone has no significant impact. These findings highlight the complexity of formative assessment as a multifaceted concept and the different impacts of formative assessment strategies on student learning. Implications for researchers and practitioners are discussed.