# **Introduction**

COVID-19 school closures led to emergency remote-learning systems almost immediately. At its peak, nearly 1.6 billion learners in more than 190 countries, or 94 percent of the world’s student population, were impacted by school closures (UNESCO 2020). Students learned less when they were remote and attending high-poverty schools, which were hit hardest (Engzell et al. 2021). Learning losses could cost this generation of students close to $15 trillion in lifetime earnings (Psacharopoulos et al. 2021). Worldwide, learning losses on average amount to 0.17 of a standard deviation (Patrinos et al. 2023), equivalent to roughly a one-half year’s worth of learning.

I estimate the impact of the duration of school closures on learning. The longer the duration of the closures, then the greater the losses. For countries with robust learning loss data, average school closures were 21 weeks, leading to average losses of 0.23 standard deviation, almost a whole year’s worth of learning. Each week of closures increases learning loss by 1 percent of a standard deviation. This will increase the education gaps between high and low socioeconomic status students (Agostinelli et al. 2022), especially in lower-income countries (Kaffenberger 2021). The main lesson learned is that if COVID continues as a low-intensity pandemic, or if a similar situation arises, keeping schools open should be a priority, as the evidence shows that the health benefits of school closures seemed to have been lower than the cost of learning losses (Allen 2022; Davies et al. 2021, 2020; Gandini et al. 2021; Lee and Raszka 2020; Ludvigsson 2020; Raffetti and Baldassarre 2022). The priority now should be to minimize the long-term impacts of school closures.

This paper contributes to several strands of the literature. First, it adds to the growing research on the impact of school closures on learning outcomes (Agostinelli et al. 2022; Belot and Webbink 2010; Haelermans et al 2022), especially on the impact of duration on learning loss (Goldhaber et al 2022; Jack et al 2022). It also adds to the literature on the determinants of school closure duration (Kurmann and Lalé 2021; Nitsche and Hudde 2022). This paper uses unique data to estimate the precise impact per week of closures on learning loss across a variety of countries. From a human capital perspective, it makes sense that school closures would lead to learning loss since schooling is a productive endeavor (Becker 1994); therefore, extending the time away from in-person instruction should lead to a reduction in learning outcomes. Programs to support learning loss mitigation have been explored.

# **1. Data**

We supplement the robust data on learning losses compiled by Patrinos et al. (2023) with a few more recent studies (see Annex 1 and https://microdata.worldbank.org/index.php/catalog/5367). Most refer to primary schooling. The number of weeks of school closure is compiled from the same studies. Not all surveys are nationally representative. In the United States, the learning loss surveys are representative, but school closure duration varied state to state, and our figure represents an average. In Nepal, the data come from a study that only includes adolescent girls from one disadvantaged district. Besides school closure and duration, other possible correlates of learning loss are included. One of those controls is the pandemic itself. We include the COVID19 death rate per 100,000 population; the lockdown stringency index; and the vaccination rate.

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