The legitimacy of authorities is paramount to their ability to exercise their powers. We examine truanting students’ and their parents’ perceptions of the legitimacy of authorities in the context of the adapted family group conference component of the Ability School Engagement Program (ASEP), a police–school partnership aimed at reducing antisocial behavior. To evaluate the program, 102 truanting students were randomly allocated to a control or the ASEP condition. Students’ and their parents’ perceptions of authorities were collected to explore how this intervention component, specifically designed to encourage legitimacy views through procedural justice, impacted perceptions of police and school staff. Results indicated that parents participating in ASEP conferences showed significant changes in their perceptions of legitimacy of authorities. ASEP parents’ perceptions of police increased following the conference, but parental perceptions of school legitimacy appeared to be affected by perceptions of the procedural justness (or unjustness) of specific authority figures in the conference. Parental views of school authorities were driven by the few school representatives who failed to engage families in procedurally just ways. Students themselves showed little change in their views following the ASEP conference, suggesting the conference alone was not sufficient for bringing about changes in student perceptions of authority legitimacy.