To balance children's right to schooling with contagion management, knowing how school re-openings affect the spread of SARS-CoV-2 is crucial . This paper considers effects on testing and positive tests for SARS-CoV-2 of re-opening Norwegian schools after a six-week closure to reduce contagion . We estimate the effect of school re-opening for teachers, parents and students using an event study/difference-in-differences design with comparison groups with minimal exposure to in-person schooling . We find no evidence that incidence increased following re-opening for either students, parents, or teachers pooled across grade levels . We find some suggestive evidence that infection rates among upper secondary school teachers increased; however, quantitatively, the effects are small and transitory . At low levels of contagion, schools can safely be re-opened when other social distancing policies remain in place.