„Schools with multiple divisions (classes) per grade level can decide to form one small class with students who need extra attention and larger classes in which easier students are put together. In that scenario it is likely to find that students in small classes do worse than students in larger classes, but this is not caused by the difference in class size but by the difference in characteristics between students assigned to small and large classes.
Univ.-Prof. Dr. Edwin Leuven u. a., „Class size and student outcomes in Europe“ (2018), S. 5