During the initial period of ‘lockdown’ in response to the COVID-19 pandemic, schools in England were closed to the majority of pupils for 15 weeks. We examine how during this time schools provided emergency remote teaching in mathematics to lower secondary pupils with different levels of prior attainment and advantage. Drawing on a mixed-methods study including a survey (N = 49) and interviews (N = 17) with Heads of Mathematics, we analyse schools’ remote learning practices and how school closures have impacted on pupils’ opportunity to learn mathematics (OTL). We find that inequitable distribution of engaged time, mathematical content and quality teaching has disproportionately negatively affected lower-attaining and disadvantaged pupils and is likely to have contributed to a widened attainment gap. We identify opportunities for HOMs to improve remote learning for subsequent school closures and enact equitable policies of distribution that improve OTL for lower-attaining and disadvantaged pupils.