COVID-19 has had worse health, education and labor market effects on groups with low socio-economic status (SES) than on those with high SES. Little is known, however, about whether COVID-19 has also had differential effects on non-cognitive skills that are important for life outcomes. Using panel data from before and during the pandemic, we show that COVID-19 affects one key non-cognitive skill, i.e., prosociality. While prosociality is already lower for low-SES students prior to the pandemic, we show that COVID-19 infections within families amplify the prosociality gap between French high-school students of high- and low-SES by almost tripling its size in comparison to pre-COVID-19 levels.