As many kids get ready to go back to school during the COVID-19 pandemic, a new study indicates ways to minimize outbreaks and their impact on in-person instruction. 

The study led by researchers from the University of Waterloo used a mathematical model to explore ways class sizes and student-to-teacher ratios can influence the number of infections and student-days of closed classrooms in Canada. The model revealed that the optimal student-to-teacher ratio required to maximize in-person instruction opportunities is below currently planned ratios in many jurisdictions, which are as high as 15:2 in childcare centres and 30:1 in schools. 

“Canadian provinces and US states are re-opening schools in the coming month, but decision-makers need to do the math and carefully consider the impact of student-teacher ratios,” said Chris Bauch, a professor in Waterloo’s Faculty of Mathematics and lead researcher on the study. “Decision-makers planning for class sizes of 30 students need to immediately reconfigure their school opening plans by switching to hybrid models, such as part in-person and part online.”

To study childcare settings, the researchers examined computer simulations of six distinct room configurations that varied in terms of the child-to-educator ratio of 15:2, 8:2 and 7:3, and family clustering, such as siblings together versus random assignment. For primary school settings, the researchers examined ratios of 8:1,15:1—which includes an approach of having students attend in alternate weeks in cohorts of 15 students each—and 30:1. 

Simulations revealed that for childcare, the configuration with a 7:3 ratio siblings together demonstrates the lowest risk, whereas centres hosting classrooms with more children, for example, 15:2, experienced three to five times as many COVID-19 cases. Across scenarios, having fewer students per class and grouping siblings together almost always results in significantly lower peaks for the number of active infected and infectious cases in the institution. Importantly, the total student-days lost to classroom closure were between five and eight times higher in the 15:2 ratios than for 8:2 or 7:3. The accelerating effect of higher student-to-teacher ratios was also apparent in the primary school setting. When more or less social distancing measures and hygiene procedures in classrooms were considered, the student-teacher ratios’ results were not significantly affected.

“The results of the model illustrate that the more students in a classroom, the more likely one of them will become infected, and therefore the more likely the classroom is to be closed,” said Bauch. “Also, when a classroom with more students is closed, it affects more students at a time. On top of this, having more students in a room facilitates transmission inside that classroom. High student-teacher ratios of the magnitude currently being planned in many school districts will result in disproportionately greater losses of in-person instruction than lower ratios.”

Co-authors of the study, Model-based projections for COVID-19 outbreak size and student-days lost to closure in Ontario childcare centres and primary schools, include Bauch, Brendon Phillips, a PhD candidate in Waterloo’s Department of Applied Mathematics, Dillon Browne, an assistant professor in Waterloo’s Department of Psychology and Madhur Anand, a professor in the School of Environmental Sciences at the University of Guelph. The study has been submitted for peer-review and publication.

Note: This research has not yet been peer-reviewed and is being released as part of UWaterloo’s commitment to helping inform Canada’s COVID-19 response.

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