We also control for national income. Since there are some reports that students in private schools lost less learning than others (Arenas and Gortázar 2022; Jack et al 2022; Wolf et al 2021), we include the proportion of private schools as a control. To gauge to what extent connectivity helped, we include individuals using the internet (percent of the population). To measure pre-existing school quality, we include the score from the World Bank’s Harmonized Learning Outcomes (HLO). To measure the strength of trade unions, we include the trade union density rate. We use the Polity5 dataset as the measure of democracy. See Table 1 for means, standard deviations, and sources.

||**Table 1**<br>|**: Means and**<br>|**Standard Deviations**<br>|
|---|---|---|---|
|Variable|Mean|Std. Dev.|Source|
|Learning loss (SD)|0.23|0.16|see Annex 1 (Learning Loss COVID-19 2020-2022)|
|Weeks closed|20.78|18.21|see Annex 1|
|Death rate/100k|152.36|125.56|Johns Hopkins Coronavirus Resource Center|
|GDP p/c $US|21709|22717|World Bank|
|Private school (%)|14.84|14.10|World Bank|
|Internet (%)|69.44|25.12|International Telecommunication Union|
|School quality|462.08|89.97|Angrist et al. 2021|
|Vaccination rate|59.77|32.17|Oxford Coronavirus Government Response Tracker|
|Stringency index|56.29|8.90|Hale et al 2021|
|Union density|22.38|16.05|International Labour Organization|
|Democracy|7.02|4.76|Polity 5|

# **2. School Closures and Learning Losses**

The literature suggests that school closures are an efficient strategy to reduce the overall duration of a pandemic (Bin Nafisah et al 2018). The decision to close down schools was primarily aimed at mitigating the spread of COVID-19 during the beginning of the pandemic (Raffetti and Baldassarre 2022). Models from previous epidemics such as influenza suggested the role of schools as places that facilitate the spreading and the possible benefit from closure (Cauchemez et al. 2008; Jackson et al. 2014). It was estimated that since school holidays could lead to a 20-29 percent reduction in the rate at which influenza is transmitted to children, then this might work for COVID-19. School closures delay the epidemic peak if implemented earlier but do not eliminate it. Imperfect knowledge led to no guidance on how long the duration of closures should be. Democratic countries tended to implement closures more quickly from the start of the pandemic than those with a more authoritarian regime (Cronert 2020).

Researchers using national data – for example, the United States national achievement test, NAEP – have shown that there is a significant correlation between the length of school closures and learning loss, confirming earlier research (Barnum 2022; Goldhaber et al 2022; Jack et al 2022; Lehrer-Small 2022; West 2022). In the United States, public schools averaged less in-person teaching than private schools. These results are explained in large part by political preferences, vaccination rates, teacher unionization rates, and local labor conditions (Kurmann and Lalé 2021). (Teacher) unionization did not necessarily always favor school closures. For example, in Greece, teachers went on strike opposing the government’s distance education plan (Lambropoulos et al 3