impacts of shocks on school dropouts, among other relevant data. The use of scenario-based simulations is not new, but it gained prominence during the pandemic as a tool to help governments assess the potential consequences of a shock of unprecedent magnitude. The main parameters of the simulation model are the following:

- **Learning gains** normally achieved during a regular school year before COVID.  The higher the expected learning gains when schools are open, the higher the learning losses when schools close. These expected learning gains have a positive correlation with countries’ income levels. The higher the income level of the country, the higher the expected learning gain. This parameter remains constant across scenarios (see Table A1 in the annex for a summary of the key input parameters on school closures, mitigation effectiveness, and school productivity (expected learning gain) used in the model to simulate the learning and earning outcomes under different scenarios).

- **Income shocks’ impact on enrollments** .  Simulations also partially capture the (much smaller) potential cumulative effects of household income shocks over the past two years on student school enrollment in primary education. This effect is negligible because evidence from both before and during COVID shows that at the primary-school level, income shocks typically have small effects on enrollment.<sup>13</sup> This component varies across countries based on country-specific enrollment-income elasticities and growth projections and remain constant across scenarios.

- **Observed duration of school closures** , which ranged from a few weeks in some countries to nearly two years in others.  We incorporate the latest country-specific school closure data, which covers two full years of schooling during COVID, from February 2020 to February 2022. As Figure 3 below shows, there are significant differences in the school-opening policies of governments around the world. This component varies across countries and remain constant across scenarios.

- **Partial closure estimates** , the share of students in a school system who are assumed to be affected by partial closures. Partial closures can be by geographic location or by certain grades or can cover all students if a hybrid model is adopted. Very few countries have been able to monitor the share of their system partially closed. This parameter varies across scenarios.

On the issue of mitigation effectiveness, the simulations assume—consistent with the observable evidence— that mitigation strategies, particularly remote learning during school closures, were typically not effective. While some governments were able to respond swiftly to school closures by providing a variety of effective remote learning modalities, many were not. Most notably, 40 percent of countries in Sub-Saharan Africa did not provide any remote learning strategy despite full or partial school closures for about one year (Muñoz-Najar et al. 2021). Even in countries that did provide remote learning solutions, the provision of remote learning did not always result in take-up by students. Surveys of schools and households reveal that many children, especially in low-income countries, were not able to engage in remote learning at all (Meinck et al., 2022; UNESCO, UNICEF, World Bank, and OECD, 2021). Some countries experienced a “remote learning paradox” where the chosen remote learning approach was not suitable to the needs of the majority of the students, contributing to this uneven take-up (Muñoz-Najar et al. 2021). Building on the above-mentioned evidence and data from access to personal computers at home, Azevedo et al 2020 (also used by Azevedo et al 2022), build a set of scenarios of mitigation effectiveness conditional on the different income levels of countries. These results yield a range of mitigation effectiveness in low- and middle-income countries from 5 to 20 percent of what an average student would learn while schools were open.

According to a survey of education ministries by UNESCO, UNICEF, World Bank and OECD (2021), over a third of low- and lower-middle income countries that provided lessons through radio or TV reported that less than half of primary school students were reached by these efforts. Even students who were able to receive

> 13 See Azevedo et al 2021 and Evans and Moskovic 2022 for a summary of that evidence.

9