Finally, it's possible to reduce the size of a class, increase student learning and still look bad compared with larger classes. This happens if, as the model suggests they should, schools put disruptive students in smaller classes. The students will learn more than they would in a larger class. Special education students, for instance, tend to be in very small classes. But they won't score as well on tests as above average students in large classes.
Schools do adjust class size to their students' characteristics.
And that's the key thing. You're reducing the class size, but not enough to offset that factor. That's what the model shows, and that's what seems to be true in the real world. Different children and different school settings have different needs. When it comes to classroom learning, one size does not fit all.