Kindergarten is an important time in a child’s life, during which children acquire and strengthen the skills needed to participate and learn in a school environment. Going to school regularly is an important part of this. Research shows that children learn more when they attend school regularly. Missing school often can make it harder for children to learn and keep up with their classmates. Children miss school for many reasons. Being sick is one of the most common reasons. However, not all children who often miss school are sick or have a long-term health condition. Research shows that many things can affect school attendance, including children’s health and behaviour, family life, their community and their school. School absences increased during the COVID-19 pandemic and have stayed high even after public health measures subsided. However, we don’t know much about how missing school in primary school is related to children’s development before and after the pandemic. Research on this topic is limited in Canada, partly because it can be difficult to collect information about school absences. It’s important to study this in kindergarten because children’s development at this age is linked to future academic and socio-emotional outcomes.Study about kindergarten absencesIn our study, we wanted to find out how often Canadian kindergarten children missed school before and after the COVID-19 pandemic.We also wanted to know whether missing school was linked to how ready children were for primary school, as captured by a measure of children’s age-appropriate abilities and behaviours known as the Early Development Instrument (EDI), assessed by kindergarten teachers for every child in their classroom. The EDI questions focus on developmental skills easily observable in the kindergarten classroom crucial for a child’s successful transition to primary school.We studied information from large groups of kindergarten children. One group attended kindergarten before the COVID-19 pandemic, and the other after the pandemic began. The study included children from publicly funded schools in eight of Canada’s 13 provinces and territories.Chronic absenteeismTeachers were asked to indicate the number of days the students in their class have been absent since the beginning of the school year. The number of days absent was categorized into two categories: zero to 13 days absent and 14 or more days absent. These categories were based on the current definition of chronic absenteeism, which is defined as missing at least 10 per cent of the school days, or two days a month. Given that EDI data were collected between February and April of a given school year, anyone absent for 14 days or more would be considered chronically absent so far in the school year.Pre-COVID and post-COVID groupsThe study included 513,159 children. Of these, 284,712 children (55.5 per cent) were in the pre-COVID-19 group and 228,447 (44.5 per cent) were in the post-COVID-19 group. The two groups were similar in many ways, including age, sex and special needs. However, after the onset of the COVID-19 pandemic, more children who were chronically absent lived in higher socioeconomic status (SES) neighbourhoods. Across Canada, chronic absenteeism increased greatly after the COVID-19 pandemic began. Before the pandemic, 17.7 per cent of kindergarten children were chronically absent; after the pandemic began, this increased to 41.3 per cent, which was more than double the rate of the pre-pandemic cohort.The increase was largest in Ontario and smallest in British Columbia. These differences may be partly related to differences in the public health measures and school policies used in each province.Unexpected resultWe also found an unexpected result. After the pandemic began, children who were chronically absent were less likely to be considered developmentally vulnerable than children who missed school often before the pandemic. This may be partly because the children who missed a lot of school changed after the pandemic. A larger percentage of these children lived in higher SES neighbourhoods. Children living in higher-SES neighbourhoods generally have better developmental outcomes.High rates of school absenteeism are generally seen as an early warning sign for schools, suggesting that children might be struggling either at school or at home. Chronic school absenteeism has historically been more common among children living in poverty or in lower SES areas. Shift in profile of chronically absent kidsThe compositional change in the group of absentee students after the onset of the COVID-19 pandemic (with more students from higher-SES neighbourhoods) may help explain why chronic absenteeism after the pandemic was associated with decreased odds of developmental vulnerability. Missing school may not have become less harmful after the pandemic. Instead, it may be that the children who were missing a lot of school were different after the pandemic. Another possible reason is that more children had access to online learning and other resources at home. These resources may have helped some children keep learning when they were not at school. Families with more resources may also have been better able to support learning at home.More research neededMore research is needed to understand why children are missing school and how this may affect their learning and development. The effects of the COVID-19 pandemic on these outcomes are still being understood. Policies aimed at reducing the number of missed days are also needed.Some level of school absences cannot be avoided. However, schools can develop ways to help children keep learning when they miss school. Helping children attend school regularly, while also supporting children and families who face barriers to attendance, will require long-term and flexible approaches that account for the diverse circumstances of students and their families.The authors do not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and have disclosed no relevant affiliations beyond their academic appointment.