24Schools are the only institution regularly reaching the majority of school-age children 25 and adolescents across the globe. Although at least 102 countries have school health services, 26 there is no rigorous, evidence-based guidance on which school health services are effective 27 42 3 48 healthy setting for living, learning and working" [1]. In 2000, WHO, the United Nations 49 Educational, Scientific and Cultural Organization (UNESCO), the United Nations Children's 50 Fund (UNICEF) and the World Bank developed a partnership for Focusing Resources on 51 Effective School Health -a FRESH Start approach [2]. The FRESH framework promotes 52 four pillars: health-related school policies, provision of safe water and sanitation, skills-based 53 health education and school-based health and nutrition services [2]. While various guidance 54 documents have been published by United Nations (UN) organizations addressing a range of 55 services from oral health to malaria [3-7], there is no internationally accepted guideline 56 regarding school health services. This systematic review of systematic reviews, henceforth 57 referred to as an overview, will inform the upcoming development of a WHO guideline that 58 addresses one pillar of the FRESH framework: school health services delivered by a health 59 provider. 60 Schools offer a unique platform for health care delivery. In 2015, the global means for 61 the primary and secondary net school enrollment rates were 90% and 65%, respectively, thus 62 the potential reach of school health services is wide [8]. Additionally, a recent review found 63 that school-based or school-linked health services already exist in at least 102 countries [9]. 64 The 2017 Global Accelerated Action for the Health of Adolescents (AA-HA!) 65 implementation guidance calls for the prioritization of school health programs as an 66 important step towards universal health coverage and urges that "Every school should be a 67 health promoting school" [10]. 68 The primary objective of this overview was to explore the effectiveness of school-69 based or school-linked health services delivered by a health provider for improving the health 70 of school-age children and adolescents. Through a comprehensive literature search, the 71 overview aimed to identify health areas and specific school health service interventions that 72 have at least some evidence of effectiveness. It was also designed to suggest further research 4 73 in areas where recent systematic reviews (SRs) exist, but with insufficient evidence. Finally, 74 the overview aimed to identify the health areas and specific school health services 75 interventions for which no SRs were found, whether because the primary literature does not 76 exist or where there are primary studies but no SR has been conducted. 77
METHODS
78This overview was conducted using the preferred reporting items for systematic 79 reviews and meta-analyses (PRISMA) [11]. A protocol was developed a priori that outlined 80 the overview objectives, aims, operational definitions, search ...