There is a consensus that students should be involved in interdisciplinary activities that promote a solid education in STEAM subjects from an early age. The outdoor settings of schools present an advantageous context for STEAM education, allowing for a myriad of learning experiences. To understand how teachers perceive the pedagogical use of the school’s outdoor space, a study was carried out in a cluster of schools in a Portuguese city, including one middle school and 10 kindergarten and elementary schools. A mixed methods approach was used, combining a questionnaire for teachers (N = 49) with interviews (N = 8). The results indicate that teachers’ perceptions of the characteristics of their school’s outdoor spaces either facilitate or hinder the implementation of outdoor pedagogical activities. Most teachers concur that the outdoors provides contact with nature and encourages interdisciplinary and collaborative activities. However, the teachers surveyed admit to using the school’s outdoor spaces only occasionally, and this use decreases as the educational level at which they teach increases. The most common use of outdoor spaces is for physical and motor activities, promoting the well-being of children and youth. Although interdisciplinary activities in outdoor spaces are recognised, their implementation is limited and hampered by factors such as the length of curricula and the lack of training for teachers in these approaches. In this sense, there is an urgent need to train teachers in the interdisciplinary use of outdoor spaces to promote a solid education in STEAM subjects.