In recent years, there has been growing pressure but also an increase of possibilities for non-governmental organizations (NGOs) to cooperate with schools in the field of global education. However, especially in cases of more continuous forms of cooperation, difficulties in process management are noted and the intended cooperation impacts often seem to lag far behind expectations. This paper uses an empirical case study that evaluated the effects of a three-and-a-half-year NGO-school cooperation on the school-internal implementation of global education to give explanations for the occurrence of such difficulties and suggest ways to support the implementation of global education via NGO-school cooperation. Against this background, the role(s) of NGOs as stakeholders for global education in the school sector will be explored.