In this contribution we will provide an overview of the developments in educational effectiveness research conducted in Belgium and the Netherlands over the past three decades (1987–2018) and discuss a selection of (mostly large-scale, longitudinal) key studies, research topics and main findings. In particular, dominant issues in the educational effectiveness research area of the aforementioned countries will be addressed, and main findings will be discussed and illustrated with results of a selection of key studies. In particular, effects of teacher behaviour and what students experience in the classroom with regard to students’ cognitive and non-cognitive outcomes will be addressed. Attention will be paid to effects of learning environment characteristics such as instructional support and class climate (i.e. learning climate, teacher-student and student-student relations), as it is clear from educational effectiveness research in general – and in Belgium and the Netherlands in particular – that these characteristics are crucial for student learning and student outcomes. Besides, these characteristics are important sources of variation. In addition, effects of group composition (also in relation to what students experience in the classroom) will be addressed. Also, attention will be paid to effects of configurations of learning environments as a holistic way to look at effects of learning environments. Furthermore, school-level factors, the connection between school-level factors and learning environment (i.e. teacher/classroom) level factors, as well as generic versus differentiated educational effectiveness, will be discussed, as well as some school level characteristics.