This study examined representations of Finnish basic education teachers’ mental models of collaboration to reveal the background features that enable or hinder changes in a school community and teacher collaboration. In this case study, we explored 41 teachers’ mental models of collaboration in a one-school community to identify and understand the features that enhance or challenge collaboration. The findings raise the question of how collaboration can support a school’s transition to a unified comprehensive school, when teachers are accustomed to working alone with a strong sense of autonomy and diverse mental models of collaboration. The findings revealed that collaboration is mainly limited to planning and sharing ideas and that teachers’ involvement in administrative work limits pedagogical discussions between teachers. Our findings suggest that the mental models examined may play a crucial role in building a school’s collaborative culture, promoting curriculum principles and developing a learning community.