COVID-19 led to strict lockdown measures, which included school closures in most countries. As a result, more than 1.5 billion students were out of school for weeks or months (UNESCO, 2022). The loss of schooling is expected to negatively impact children's cognitive development, even if distance learning modes are enacted. The loss of in-person teaching could also lead to inequality since the only remaining relevant input is parental involvement during school closures (Agostinelli et al., 2022). Most studies document significant learning loss. In Europe, the average learning loss is almost a quarter of a school year, but the estimates are available mainly for Western European countries (Donnelly and Patrinos, 2021). Worldwide the loss is even greater, especially in lower-income countries (Patrinos et al., 2022). Poland is an interesting case because it represents countries in Eastern Europe where school closures lasted longer, and research on learning loss is scarce.

To properly estimate the effect of school closures and to distinguish it from the effect of the 2016 structural changes, we compare the expected and actual achievement of three cohorts of students in secondary schools. We assume students should gain a minimum of 0.1 standard deviation (SD) during one year of education. That is a safe assumption but in line with previous studies comparing 15, 16, and 17-year-old student results on the PISA scale in Poland (Jakubowski et al., 2022). International evidence indicates the gains should be larger, around 0.2 SD, which would make our results more significant as they increase the expected achievement (Avvisati and Givord, 2021). We also assume students tested in autumn (10th grade in TICKS 2021) have a similar achievement to those tested one grade below in the spring (9th-grade assessment in PISA 2003-2018). Assuming any achievement progress between spring and autumn makes our results even more significant.

The Polish success story of rapid social and economic progress relied strongly on human capital improvement. Unfortunately, this factor is now under significant distress. Significant learning losses have been experienced by Polish students due to the COVID-19-induced school closures. In mathematics and science, the learning losses are equal to more than a year's worth of schooling, even though schools were closed for only part of an academic year. In addition, we show that the 2016 reforms also had a negative impact on student learning. These skills losses are likely to affect the future economic success of the students as well as the country as a whole. Future earnings are projected to decline by PLN 74,693 (more than US$15,000) per year for the affected students. The country would then lose the equivalent of 7.2% of GDP over time.

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