Mixed‐aged (MA) classes are a common phenomenon around the world. In Sweden, these
types of classes increased rapidly during the 1980s and 1990s, despite the fact that existing
empirical support for MA classes is weak. In this paper, the effect of attending an MA class
during grades 4–6 on students' cognitive skills is estimated. Using a unique survey with
information on students, parents, and teachers, it is possible to control for many factors that
could otherwise bias the results. A negative effect on short‐run cognitive skills, as measured …

Mixed-aged classes (MA-classes) are a common phenomenon around the world. In
Sweden, these types of classes increased rapidly during the 1980: s and 1990: s. But the
scientific evidence of the benefits of MA-classes is not convincing. In this paper, we estimate
the effect of attending an MA-class during grades 4–6 on students' cognitive skills. Using a
unique survey with information on students, parents and teachers, we are able to control for
many factors that could otherwise bias the results. We find a negative effect on the short-run …