The COVID Social Mobility & Opportunities (COSMO) study is a new national cohort study generating high-quality evidence about how the COVID-19 pandemic has affected socio-economic inequalities in life chances, both in terms of short- and long-term effects on education, wellbeing, and career outcomes. A representative sample of young people in England who were in Year 11 in the 2021/2022 academic year were invited to take part in the survey, with the aim of following them as they progress through the final stages of education and into the labour market. This second brief finds that many students missed a large amount of school time during the pandemic, even after schools had re-opened nationally; that many young people feel they have fallen behind due to the pandemic; and that 53% of young people took part in at least one type of 'catch-up' activity. [For the first brief, "Lockdown Learning," see ED625712. For the third brief, "Future Plans and Aspirations," see ED625715. For the fourth brief, "Mental Health and Wellbeing," see ED625716.]