This study aimed to explore changes in mental health outcomes (depression, anxiety, home,
and school stress) from before the first COVID-19 wave (autumn 2019) to the later stages of the
same wave (autumn 2020) in a sample of N = 377 Swiss adolescents (Mage = 12.67; 47% female. The results showed that the expected impact of the pandemic on mental health was not
noticeable in the later stages of the first COVID-19 wave. Only two effects were demonstrated in
terms of intra-individual changes, namely, an effect of gender on depression and anxiety symptoms
and an effect of reported COVID-19 burden on school stress symptoms. Moreover, few associations
were found for selected predictors and students’ mean level scores, averaged across both time points.