2. Exclusion criteria.

Population	Populations not at risk of becoming infected with COVID‐19 Studies not targeting human transmission
Setting	Schools whose main focus is on caring for rather than providing education to young children (e.g. early child care such as daycare or nurseries) Kindergarten, where the primary purpose is childcare rather than education (e.g. in Germany) Schools targeting adults (e.g. adult education centres, trade schools, professional schools) Universities, colleges or other institutions providing tertiary education
Interventions	Interventions not related to COVID‐19 All COVID‐19‐related interventions not implemented in the school setting, including a range of containment and mitigation measures (e.g. community‐based quarantine, personal protective measures, hygiene measures, bans on mass gatherings and other social‐distancing measures)
Study designs	Empirical studies without quantitative measures (e.g. qualitative studies) Diagnostic studies only reporting diagnostic accuracy measures Non‐empirical studies (e.g. commentaries, narrative and systematic reviews)