%0 Journal Article %T Effects of a Data %A Adrie J. Visscher %A Emmelien A. van der Scheer %J Journal of Teacher Education %@ 1552-7816 %D 2018 %R 10.1177/0022487117704170 %X Data-based decision making (DBDM) is an important element of educational policy in many countries, as it is assumed that student achievement will improve if teachers worked in a data-based way. However, studies that evaluate rigorously the effects of DBDM on student achievement are scarce. In this study, the effects of an intensive DBDM-intervention for Grade 4 teachers on students¡¯ mathematical achievement were investigated in a randomized controlled trial. Multilevel analyses showed that although no main effect on students¡¯ mathematical achievements was found, students who received ¡°extended instruction¡± benefited significantly from the intervention. Based on the results, recommendations for the design of new DBDM-interventions and for their evaluation are presented %K data-based decision making %K professional development %K mathematics %U https://journals.sagepub.com/doi/full/10.1177/0022487117704170