Citizenship education is historically linked with political developments that have forced governments to think deeper about nationality, power, identity, and the process of decolonization since large sectors of the population are denied and even excluded from the development of their citizenship. Currently, there is a need to provide mechanisms that foster the development of students' citizenship by enabling them to position themselves critically, politically, responsibly, and constructively in their own sociocultural contexts. These mechanisms contribute towards offering the intellectual tools needed to participate in society and also can encourage educators to develop pedagogical actions that stimulate students to develop their citizenship and be aware of problems they face in their communities. Thus, results of a study conducted in a public middle school, located in the metropolitan region of Belo Horizonte, Brazil, with 12 eighth-grade middle school students enrolled in a state public school, who are residents in a peripheral community, showed how ethnomodelling contributed to the development of mathematical content, which helped them to understand and propose solutions to the lack of basic sanitation. We concluded that competencies to analyze, decide, and judge solutions through the elaboration of ethnomodels helped students to make decisions to local and global problems, which promoted the development of their citizenship as well as the acknowledgment that the denial and exclusion process of peripheral communities' members still prevails in modern society.