Background: This paper investigates how the COVID-19 school closure has affected the gender gap in grade-8 students' performance and what are the drivers behind this. By analysing four different countries (i.e., the Russian Federation, Slovenia, Uzbekistan and the United Arab Emirates), the paper represents the first study addressing the issue from a comparative perspective. Methods: The study uses data from the Responses to Educational Disruption Survey (REDS) survey, which comprises international comparable data on how students approached remote learning during the COVID-19 disruption. The extent of the gender gap is estimated by employing an ordered logit model, while the Karlson-Holm-Breen (KHB) decomposition method is used to analyse the different potential channels that could account for the gender gap during COVID-19. Results: The empirical results reveal that, during the COVID-19 school closure, girls tended to perceive changes in their learnings less favourably than boys, both in terms of improvement in self-perceived learning and self-reported improvement in grades--with odds of a more affirmative response between 20 and 25% lower for girls relative to boys. The main drivers explaining this gender gap are physical activity and psychological distress of students during the COVID-19 disruption, as well as the perceived family climate. Conclusions: The paper shows systematic gender differences in how students perceived their educational outcomes changed due to the COVID-19 disruption, providing evidence on the factors driving these differences. The findings could be employed to design policy actions aimed at increasing gender equality in education.