As schools evolve into open systems interacting with a variety of stakeholders, the role of parents is increasingly viewed as extending beyond that of mere supporters to co-designers of public education. However, most previous studies have focused on the impact of parental involvement on school satisfaction or teacher trust, with relatively few empirically examining how such involvement affects teachers themselves. This study investigates the influence of parental participation in school decision-making on teachers’ trust in parents. The findings reveal that in schools where a participatory decision-making climate among parents is well established, teachers exhibit significantly higher levels of trust in parents. Notably, this trust correlates more strongly with parents’ respect for teachers than with their involvement in learning support. These results suggest that participatory parental decision-making serves not only as a signal of shared responsibility for student education, but also as a relational signal through which teachers feel their professional judgment and roles are recognized. Based on these findings, the study offers policy implications: (1) the need to establish institutional support to ensure parents’ substantive participation in school affairs, and (2) the importance of teacher training aimed at improving perceptions of parental roles.