The aim of this study was to implement the project "Mobilize Cooperation to Develop to Be the Classroom of the 21st Century in Sarakulnawitaya School ", which is one of the research projects that is related to education in the 21st Century, using the Participatory Action Research (PAR) methodology consisting of Planning, Acting, Observing, and Reflecting (PAOR) for two cycles. Each Cycle lasted one semester during the Academic Year of 2022. The expected outcome was to promote changes, learning, and the knowledge gained from practice. The research participants consisted of seven teachers and administrators, two community leaders, three parents of students, and three school supporters. A total of 50 students received benefit from the development. The results from the comparative practice of three periods (before the first cycle, after the first cycle, and after the second cycle) showed the following: (1) there had been improvements in the implementation of the work and in the quality of classrooms aligned with the ideas of the 21st Century; (2) the research team, the research participants, and the school gained various learning experiences, especially in: (a) building networks with communities and related organizations, (b) creating sustainable relationships, and (c) achieving successful work outcomes; and (3) knowledge gained from practice demonstrated the causal relationship between the driving force used to promote change, the resistance to change, the methods used to overcome the resistance to change, and the resulting outcomes, which is the prototype model called "Mobilize Cooperation to Develop to Be the Classroom of the 21st Century in Sarakulnawitaya School."