remote-learning systems almost immediately. In response to this disruption, education researchers are beginning to analyze the impact of these school closures on student learning progress or lack thereof. The term _learning loss_ is commonly used in the literature to describe declines in student knowledge and skills (Pier et al. 2021). Historic data provides researchers with information regarding where student learning should be year over year and is often measured through regular testing. Learning loss occurs when educational progress does not occur at the same rate at which it has historically compared to previous years.

School closures have a large, persistent, and unequal effect on learning. Long-term, nationwide school closures result in learning losses (see, for example, Belot and Webbink 2010). In turn, learning losses can lead to decreased future employment potential and lower earnings (see, for example, Chetty et al. 2014; Currie and Thomas 2001; Psacharopoulos et al. 2021). Online education is an imperfect substitute for in-person learning, particularly for children from low-income families. Peer effects also change: schools allow children from different socioeconomic backgrounds to mix, and this effect is lost when schools are closed. Another factor is the response of parents, some of whom compensate for the changed environment through their own efforts, while others are unable to do so. All this leads to the finding that school closures have a large, persistent, and unequal effect on human capital accumulation (Agostinelli et al. 2022). The channels operating through schools, peers, and parents all contribute to growing educational inequality during the pandemic.

As a result of the first wave of lockdowns and school closures beginning in March 2020, on average, a student has lost about one-third to a half a year’s worth of learning. The magnitude of our findings appears to validate scenarios projected by the World Bank (Azevedo et al. 2021). This has consequences in terms of further education as the lost learning may impact opportunities for higher levels of schooling. There are also long-term future earnings losses associated with lost human capital, with students potentially losing trillions of dollars in future incomes.

# **Data**

The just-released PIRLS 2021 data include results for 65 countries and benchmarking participants. This is the first international picture of student achievement after the COVID-19 pandemic.

Our analysis uses data from 24 education systems of the European Union (22 countries and separate data for the Flemish and French parts of Belgium) and for an additional 7 countries when providing results for all ECA+ countries. We compare PIRLS results from assessment rounds in 2001, 2006, 2011, 2016 and 2021. Overall, our sample includes 582,112 students (459,039 in EU countries) participating in all rounds of PIRLS, representing data for nearly 30 million 4<sup>th</sup> grade students across 20 years. The sample from 2021 – the post-COVID-19 data – includes 157,167 students (120,895 in EU countries), representing the results of nearly 7 million 4<sup>th</sup> graders in ECA+ countries (4 million 4<sup>th</sup> graders in the European Union).

PIRLS data include the plausible values measuring reading achievement and information on student socio-demographic characteristics (e.g., age, grade, and gender). In addition, school principals surveyed by PIRLS provided details on how instruction was affected by COVID-193