This article aims to explore the contribution of action research to the development of active participation of pupils in the context of the sustainable school. Action research is looked at not simply as a methodological tool for the exploration of participation, but as a key element of the educational actions that promote the active participation of pupils. Educational research was conducted during a school year at a primary school in Lavrio, Greece, with the participation of two teachers and the pupils of two classes (the upper grades--fifth and sixth). Action research methodology facilitated the critical, reflective, and, at the same time, organized a systematic exploration of the active participation of pupils. Its contribution to the objective of the research, that is, enhancing active participation of pupils, was also fundamental. As is clearly reflected in the research data, action research helped pupils participate actively and improve their participation, addressing the difficulties they identified.