This policy white paper examines psychosocial factors associated with mental health among high school students in the United States. Data were collected from 91 predominantly U.S.-based high school students through an anonymous psychosocial check-in administered during a national mental health and college and career readiness webinar hosted by ACT, a U.S.-based standardized testing organization, in May 2023. In this sample, 62% of students reported moderate or serious psychological distress based on the Kessler Psychological Distress Scale (K6), a widely used brief screening measure. Using validated measures of psychological distress, well-being, perceived social support, belonging, and growth mindset, regression analyses examined which modifiable psychosocial factors were most strongly associated with student mental health outcomes. Psychosocial predictors collectively explained 44% of the variance in psychological distress and 26% of the variance in well-being. Family support emerged as the strongest independent predictor of lower psychological distress, while school-related belonging also demonstrated unique associations. Findings underscore the prevention relevance of strengthening family-linked and school-based protective factors within secondary education systems. The report outlines policy-relevant recommendations aligned with prevention-oriented public health models, the Every Student Succeeds Act (ESSA), and multi-tiered systems of support (MTSS) frameworks.