Answering the question of effectiveness of educational interventions is no easy task for a multitude of reasons. The effectiveness of an intervention depends not only on the intervention itself but also, for example, on the target group, the available infrastructure, the current legislation, the time of implementation or the expertise of the teachers. This special issue shows the diversity in the goals pursued and the interventions used to achieve them. It also shows methodological differences in effectiveness research and argues the need for nuanced interpretation and for explicitly considering the context for the intervention.