With 1 in 4 youth experiencing mental illness in Australia, the escalating demand for mental health promotion within schools necessitates an examination of the efficacy and practical utility of an exemplary positive education program (PEP) to improve mental health and optimise learning. Given that government schools in Australia continue to educate the greatest proportion of youth today, it is crucial to understand the contextual needs and identify relevant aspects of best-practice PEPs (Geelong Grammar School’s Year-10 PEP), to determine the suitability for implementation in public schools. This longitudinal study identified factors influencing program success in both independent and public schools. There were significant improvements over time compared with well-being as usual comparison groups, for psychological well-being and ill-health. There were also significant improvements over time for both groups, for social relationships, school engagement and accomplishment with improvements being most salient at the 6-month follow-up rather than at the immediate post-program stage. This finding is consistent with the results from the independent schools and shows that for many PEP evaluation studies, measuring outcomes only at immediate post-intervention, might be missing the positive outcomes that take some time to manifest, due to the applied nature of positive education, possibly around 6 months.