Background: Adolescence coincides with the adoption of health behaviors that schools are not necessarily equipped to properly address. Collaboration between schools and external health services such as public health could fill gaps in addressing student health. Methods: The current study uses student- and school-level survey data from 59 nonprivate secondary schools in Ontario, Canada in year 6 (2017-2018) of the COMPASS study to examine barriers to improving student health, and analyze the effect of public health engagement on student health behaviors. Results: The majority of schools have received resources from their local public health unit, however, less than one third of schools were developing/implementing programs jointly, and 12% of schools reported no engagement. Students had higher odds of better overall mental health, of meeting screen time guidelines, and were less likely to bully others if public health units solved issues together with schools regarding these health behaviors. Conclusions: There is a notable lack of consistent public health engagement in schools participating in the COMPASS study despite a need for such services. Creating mechanisms to develop and strengthen effective partnerships between schools and external service providers such as public health might alleviate some barriers to implementing health interventions in Ontario secondary schools.