Co-Primary End-Points: 1. Number of school days missed among those eligible to be in school during the 9-week period of the study. Daily school attendances will be obtained from the school register and absences recorded with reconciliation with COVID-19 associated absences. This will be compared between study arms; to historic schools’ data; and to national schools’ benchmark data collected via a survey of non-participating schools. 2. Estimated number of in-school COVID-19 transmission events during the 9-week period of the study: the number of positive cases will be obtained from the following sources: 2.1. Weekly LFD active case finding (control and intervention arms) during the 9-week period of the study 2.2. Symptomatic individuals’ NHS Test and Trace results obtained from Community Testing routine data (control and intervention arms) during the 9-week period of the study 2.3. In-school LFD DCT testing (intervention arm) during the 9-week period of the study Positivity rates will be reported for each source separately to facilitate like-for-like comparison between arms Epidemiological links between cases will be obtained from the NHS Test & Trace Contact Tracing and Advice Service database. Additional links will be obtained by membership of school-reported contact groups. Onward transmission from the index case will be determined by the following: 1. Genomic sequence of virus: the additional PCR swab collected from positive individuals will be used to determine the whole genomic sequence of isolates. A sample of apparent links will be assessed with comparisons of whole-genome sequencing. The diversity of genetic sequences both in the schools and the community (routinely determined by COG) will be used to help interpret the results. Preliminary work currently undertaken will determine the appropriate genetic distance to be used to exclude a direct transmission event between individuals. This is likely to be two SNPs. 2. Plausible epidemiological link (e.g. membership of same close contact group) 3. For positive individuals identified in DCT the DMIC will review all available data to determine if the individual’s infection was likely to have resulted from onward transmission from the index case; or via co-infection from an unknown ‘upstream’ positive or out-of-school positive case.

Co-Primary End-Points: 1. Number of school days missed among those eligible to be in school during the 9-week period of the study. Daily school attendances will be obtained from the school register and absences recorded with reconciliation with COVID-19 associated absences. This will be compared between study arms; to historic schools’ data; and to national schools’ benchmark data collected via a survey of non-participating schools. 2. Estimated number of in-school COVID-19 transmission events during the 9-week period of the study: the number of positive cases will be obtained from the following sources: 2.1. Weekly LFD active case finding (control and intervention arms) during the 9-week period of the study 2.2. Symptomatic individuals’ NHS Test and Trace results obtained from Community Testing routine data (control and intervention arms) during the 9-week period of the study 2.3. In-school LFD DCT testing (intervention arm) during the 9-week period of the study Positivity rates will be reported for each source separately to facilitate like-for-like comparison between arms Epidemiological links between cases will be obtained from the NHS Test & Trace Contact Tracing and Advice Service database. Additional links will be obtained by membership of school-reported contact groups. Onward transmission from the index case will be determined by the following: 1. Genomic sequence of virus: the additional PCR swab collected from positive individuals will be used to determine the whole genomic sequence of isolates. A sample of apparent links will be assessed with comparisons of whole-genome sequencing. The diversity of genetic sequences both in the schools and the community (routinely determined by COG) will be used to help interpret the results. Preliminary work currently undertaken will determine the appropriate genetic distance to be used to exclude a direct transmission event between individuals. This is likely to be two SNPs. 2. Plausible epidemiological link (e.g. membership of same close contact group) 3. For positive individuals identified in DCT the DMIC will review all available data to determine if the individual’s infection was likely to have resulted from onward transmission from the index case; or via co-infection from an unknown ‘upstream’ positive or out-of-school positive case.