Suicide among school-age children is a serious issue in Japan, exacerbated by the coronavirus disease 2019 pandemic. Collaboration and cooperation between schools—where children spend much of their time—and medical/welfare services are indispensable. However, teachers are overworked, and intensified stress levels have led to high absenteeism. We propose the effective use of the Observe–Orient–Decide–Act (OODA) loop for timely collaboration and cooperation between schools and medical institutions to manage high-risk children as a measure to prevent suicide. We administered questionnaires to 205 teachers who worked with children, nurses, welfare professionals, and school counsellors in schools and related facilities; 171 respondents with valid responses were included. We examined their self-rated health, attitudes towards the OODA loop, levels of depressive symptoms, satisfaction/dissatisfaction with the current status of collaboration and cooperation, and reasons for this. When we compared those satisfied/dissatisfied with the current status of collaboration and cooperation, we found no significant differences in the level of depressive symptoms, but the self-rated health of the latter was poorer. We identified three factors in the attitude survey on the OODA loop—flexible and independent situational assessment, group monitoring and sharing, and self-monitoring—and those who were dissatisfied showed lower scores for all items. We classified the reasons into three categories—details of collaboration and cooperation, methods of collaboration and cooperation, and organisations for collaboration and cooperation—revealing marked differences. The level of satisfaction with the current status of collaboration and cooperation was correlated with the level of mental health. Satisfied participants were more positive about adopting OODA perspectives. Raising awareness of the OODA concept among teaching personnel, creating an organisational structure, establishing systems for appropriate and organic collaboration between schools and medical/welfare institutions, and reviews by external institutions are necessary to effectively use the OODA loop.