Socio-economic disparities in academic achievement have been repeatedly reported in the past (Coleman et al., 1966; Mullis et al., 2023). Accordingly, the continuous monitoring of these disparities is an important objective of international large-scale assessment studies. An established approach to efficiently measure students’ socio-economic background is to ask them about the number of books at home (Hanushek & Woessmann, 2011). Recently, however, doubts have been raised as to whether this variable is still a valid indicator of socio-economic status (Heppt et al., 2022; Schwippert, 2019). As printed books can be replaced by digital alternatives such as e-readers, audiobooks, or tablets, their absence no longer necessarily indicates lower levels of prosperity, education, and appreciation of reading. Conversely, owning books despite numerous digital substitutes could indicate a particular level of affluence and appreciation of reading. Against this background, the present contribution examined if the number of books at home changed in the period from 2001 to 2021. Furthermore, the development of the relationship between the book variable and parental education, as well as academic achievement was investigated. To examine these research questions, data from N = 429,292 students from 18 (predominantly Western) countries that participated continuously in the Progress in International Reading Literacy Study (PIRLS), conducted every five years from 2001 to 2021, were used. The samples from the participating countries were drawn in such a way as to be representative. In addition to the number of books, which was measured using an ordinal 5-point scale, the highest level of education attained by the parents and the students’ reading literacy were included in the study. The results showed that, across all countries, the proportion of households with more than 100 books declined between PIRLS 2001 and 2021. The difference between 2001 and 2021 was statistically significant. However, country-specific trend patterns emerged: More specifically, twelve countries saw a decrease of the proportion of households with more than 100 books, five countries showed a rather stable development, and one country saw an increase. Regardless of this, both, the correlations with parents’ educational attainment and with academic achievement showed a slight, statistically non-significant increase across all countries, with similar patterns emerging in the different countries, but also some notable differences in terms of the strength and variation of the relationships. Overall, the results suggest that the number of books remains a valid indicator of students’ socio-economic background. Limitations and implications for future research are discussed.

Coleman, J. S., Campbell, E. Q., Hobson, C. J., McPartland, J., Mood, A. M., Weinfeld, F. D., & York, R. L. (1966). Equality of Educational Opportunity. US Government Printing Office. Hanushek, E. A., & Woessmann, L. (2011). The Economics of International Differences in Educational Achievement. In E. A. Hanushek, S. Machin, and L. Woessmann (Eds.), Handbooks in Economics, Vol. 3 (pp. 89-200). North-Holland. Heppt, B., Olczyk, M., & Volodina, A. (2022). Number of Books at Home as an Indicator of Socioeconomic Status: Examining its Extensions and their Incremental Validity for Academic Achievement. Social Psychology of Education, 25(4), 903-928. https://doi.org/10.1007/s11218-022-09704-8 Mullis, I. V. S., von Davier, M., Foy, P., Fishbein, B., Reynolds, K. A., & Wry, E. (2023). PIRLS 2021 International Results in Reading. Boston College, TIMSS & PIRLS International Study. https://doi.org/10.6017/lse.tpisc.tr2103.kb5342 Schwippert, K. (2019). Was wird aus den Büchern? Sozialer Hintergrund von Lernenden und Bildungsungleichheit aus Sicht der international vergleichenden Erziehungswissenschaft. Journal for educational research online, 11(1), 92-117. https://doi.org/10.25656/01:16789