By mid-April, 2020, school closures had impacted 94% of the world's students, with the duration and impact of closures varying substantially by country.1 As new variants rise and fall, it is vital to understand ways to minimise both educational and social disruption by keeping schools open while also reducing the spread of infection. The results are informed by pre-pandemic data on contact patterns, collected via radio frequency identification tags (wearable sensors that detect proximity), and infection data from pilot screening trials in French primary and secondary schools. Colosi and colleagues use the infection data to estimate the effective reproductive number in schools during the alpha (B.1.1.7) and delta (B.1.617.2) variant waves, informing transmission in an individual-based model of infections that is structured according to the contact pattern data.