„An increase in frequency of being absent is highly related to a decrease in average achievement, especially for students absent ‚once every two weeks‘ or more. For example, the average mathematics score in eighth grade decreased from 502 for students ’never or almost never‘ absent to 495 for students absent ‚once every two months‘, to 475 for students absent ‚once a month‘, to 452 for students absent ‚once every two weeks‘, and to 412 for students absent ‚once a week‘ – a 90-point difference between regular attendance and missing school very often.“
IEA (Hrsg.), TIMSS 2019. International Results in Mathematics and Science (2020), S. 407.