Formal achievement data such as test scores and school performance feedback from standardised assessments can be a powerful tool for data-based decision making and school improvement. However, teachers' and school leaders' usage of these data is not necessarily straightforward or predictable. In order to illuminate how educational professionals engage with data in their daily practice, from their own subjective backgrounds and within their own contexts, data use researchers increasingly adopt a sensemaking perspective. Sensemaking, a theoretical construct grounded in psychological and organisational scholarship, offers a framework and a vocabulary to explain how cues such as educational output data are processed in real-life educational settings. As such, sensemaking research sheds light on reasons why educational professionals' use of these formal achievement data may deviate from normative expectations. The present study is a conceptual review of how sensemaking is conceived and applied in literature on educational professionals' use of formal achievement data. In total, 25 empirical and theoretical studies were selected and subjected to thematic analysis. Findings include that sensemaking is used as a lens to study data use, as well as a label for interpretive micro-processes of data analysis and interpretation, and that formal achievement data can be regarded as sensemaking resources. An integrated conceptual framework on educational professionals' sensemaking of formal achievement data is presented, including a discussion of critical insights that may inspire future research on data-based decision making in education.