To enhance sustainable and walkable cities we need to know which aspects of the urban environment affect children’s walkability and working on measures related to communication and education to ensure widespread awareness in society as a whole. The aim of this paper is to advance the implementation of participative and dynamic techniques at university level and targeting children from a sustainable mobility perspective. Through the Service-Learning project “Let's Walk Safely to School!” three specific objectives – related with learning, service and teaching are addressed. While learning, university students conducted a community service and resolved several challenges related with complementary skills for pedestrian mobility and Geographic Information Systems, while children learn mobility concepts. Its development combines the resolution of a challenge, learning by doing – since the whole process was carried out in a real context –, and cooperative learning. Using the results of a survey of 200 children studying in a school in Madrid, field work, and digital mapping, eight University students developed an interactive web map which classifies the streets around the school according to the children’s comfort level, safety/security and ease of travel. The participants broadened their academic competencies, while exchange skills, knowledge and expertise, and also acquired transversal competencies related to teamwork, organisation and planning, effective communication and knowledge of ICTs.