The value of urban green space for environmental education fieldwork is empirically investigated in a study among all secondary schools in Amsterdam. The article describes how the proximity of schools to green spaces emerges as a new factor in the "sustainable city" and the "compact city" debate. For fieldwork excursions proximity to green spaces is crucial for establishing a pattern of outdoor environmental education. Once established, it shapes teachers' attitudes on excursions. A linear structural path analysis reveals how this in turn results in more fieldwork excursions to other destinations. Interviews with teachers show how this can be interpreted mainly as a result from iterative positive experiences with excursions close to the school, which are triggered by the availability of nearby green space. Remarkably, beside the effects of green spaces for well-being and health, the significance of green space for environmental education of children remained under-investigated. This argument came prominently to the fore in a case of urban densification within the framework of compact city policies. In the dispute about the elimination of green space, citizens claimed a high educational value would vanish, but they felt this value was not recognized in the decision-making process.