Green spaces in cities play an important role in people's social, economic and physical well-being. Children spend a large proportion of their time at school, and to date there have been no studies that have investigated the proximity of schools to green spaces. In this work, we conducted a nationwide assessment of the green spaces surrounding 186,080 schools in Brazil, which includes more than 40 million students. We estimated that about 46,000 of Brazil's schools (~25%; about 9 million students in total) are located in regions with high greenness exposure. We also found that public schools, low-income areas, low-population areas, and areas with good educational indicators were more likely to have high levels of green space around schools. Information about schools exposure to environmental features has prompted public and private policy to promote health by making schools healthier. Our findings can inform public policy to enable targeted interventions that protect Brazilian students from environmental hazards and improve their safety, health, and learning performance. This study provides new insights into a particular aspect of the school environment (green spaces) that may be relevant to urban planners and policy makers in both developed and developing countries.