Data literacy is assumed to be a precondition for the effective implementation of data-based decision making in schools. This study was aimed at investigating changes in 1182 educators' data literacy with regard to student monitoring system data, during a 2-year intervention, which was assessed by using a pretest and posttest. A multivariate multi-level IRT analysis was conducted. The multivariate approach enabled the identification of differences in initial data literacy and development, based on educators' characteristics. Findings showed significant improvements in educators' data literacy. Furthermore, the ‘knowledge gap’ between educators with a master's degree versus higher education was closed, just as the gap between teachers and school leaders.