This paper investigates aspects of content knowledge related to teaching and learning about solid waste, focusing on the processes of learning and teaching by Elementary School teachers in Brazil, in two modalities of continuing education: courses and school-based meetings. We analyse elements of teachers' reflections whilst referring to three dimensions of environmental education: knowledge, values (ethic and aesthetic), and political participation. We identify which dimensions are predominant, or absent, and the aspects included and developed in projects elaborated by teachers. The results raise issues we consider important to support teacher education and curriculum programmes and help teachers develop more substantial, critical and effective projects about the subject. (Contains 1 table.) [This research was supported by the Conselho Nacional de Desenvolvimento Cientifico e Tecnologico (CNPq) and the Fundacao Coordenacao de Aperfeicoamento de Pessoal de Nivel Superior (CAPES).]