Physical activity has a variety of health benefits for young people. The World Health Organization (WHO) recommends that children and adolescents aged 5–17 years should be physically active for at least 60 min a day. This Health Impact Assessment (HIA) examined the potential impact of a daily physical activity unit in Austrian schools, with a focus on children and adolescents up to eighth grade. The HIA methodology systematically followed several stages: screening and scoping, appraisal, and formulation of recommendations. A literature review, an online survey (n = 712), focus group discussions (n = 4), and appraisal workshops (n = 2) have been carried out. The analyzed results indicate a primarily positive impact on the individual health of children and adolescents, on social and community-related networks, on living and working conditions, and on the system level. Recommendations for the implementation include ensuring equal opportunities and support for disadvantaged children and schools. Furthermore, the comprehensible selection of pilot regions and the nationwide resource planning should be considered. Additional important factors include the education and further training of pedagogical staff and coaches, and the availability of sufficient infrastructure. In the long term, the fixed integration of five additional teaching units of physical activity per week, and an increased focus on the elementary/nursery school sector were identified as significant.