Using data from a computer-based formative feedback system, we compare learning gains in the 8 weeks of school closures related to the COVID-19 pandemic in Switzerland with learning gains in the 8 weeks before these school closures. The school performance in mathematics and language of N =28,685 pupils is modelled in second-order piecewise latent growth models with strict measurement invariance for the two periods under investigation. While secondary school pupils remain largely unaffected by the school closures in terms of learning gains, for primary school pupils learning slows down and at the same time interindividual variance in learning gains increases. Distance learning arrangements seem an effective means to substitute for in-person learning, at least in an emergency situation, but not all pupils benefit to the same degree.