In current empirical educational research, one important question is how the societal measures taken to contain the COVID-19 pandemic affected students' cognitive development. This also raises the question whether disadvantaged student groups suffered particular disadvantages in their cognitive development depending on their individual characteristics or family background. We analyzed a data set of 104 students of three Austrian elementary schools (Grade 3). Students' basic cognitive abilities were assessed by two subscales (inductive reasoning, numerical thinking) of the Cognitive Abilities Test 1-3 (KFT 1-3; Heller and Geisler 1983). We also analyzed effects of students' individual characteristics and indicators of their home learning environment. Basic cognitive abilities were assessed at the beginning and end of the 2020/21 school year and thus before and after societal and school-related measures to contain the second and third pandemic waves in Austria (including contact restrictions, school closures, distance learning and quarantine measures). According to intelligence research (Rindermann 2011), an age-appropriate development in students' mean test performance of about d = 0.40 would have been expected over the nine-months study period. Empirically, however, there were no significant changes in the average and heterogeneity of students' test performances. At the same time, children from homes with a higher parental educational background and those with more digital devices and internet access showed a significantly higher development. The findings thus indicate that, on average, the children did not develop as positively in the school year characterized by pandemic containment measures as would have been expected. Beyond this, our results indicate cognitive losses among disadvantaged student groups., (© The Author(s) 2022.)