A collective design pedagogy is an idea for a socially engaged learning practice that involves schoolchildren in the production of their city. How can children be involved in (re)designing their environment and work with the wider community, to democratize the city and develop practices of responsible citizenship? The case study is situated in Mumbai, where the changing population, economy and environment have created a need for more child-centred learning activities and pedagogical innovation. In collaboration with education NGO Muktangan School and the neighbourhood Mariamma Nagar, the research sets out a series of pedagogical experiments investigating the city’s potential to house socio-spatial active citizenship practices by children, school staff and the community, between 2012 and 2017. Four series of workshops included the same class of schoolchildren in observing, assessing and then transforming their environment. Using activities borrowed from architectural practice, they transformed their school and neighbourhood by designing interventions. Critical pedagogical, constructivist and co-design methods included the children in activating what Henri Lefebvre called the right to the city; the development of a collective design practice fuses learning with the environment. Children can become active citizens through design and work with local craft as a political design tool. The children identified well-being as the overarching itinerary for their design projects: they designed responses to problems such as open gutters, mosquitoes, fighting and bad language, lack of green spaces and insufficient waste management. This paper argues that children’s role as architects is pedagogical: with facilitation, they can be involved in the production of their current environment, develop their political identity, and foster their ability to communicate ideas. Co-design allows children to develop empathy, think critically and learn how to learn.