The COSMO study is a longitudinal youth cohort study initiated following the onset of the COVID-19 pandemic to examine the unequal impacts of the pandemic and its aftermath on the life chances of a generation of young people. The study included over 13,500 students who were in Year 11 during the 2020-21 academic year across over 500 schools in England, recruited from the National Pupil Database with additional private school sampling. The study disproportionately sampled young people from disadvantaged, ethnic minority and other hard-to-reach groups to ensure it reflects the full range of experiences of the pandemic.