noun
combined class; multi-grade class
Educational term for a class where students from two or more grade levels are taught together, typically in small schools.
この小さな学校では、複式学級で授業を行っている。
In this small school, classes are conducted as combined classes.
単式学級 is a single-grade class, the standard arrangement in most schools, while 複式学級 combines multiple grades.
Compound of 複式 (combined system) and 学級 (class). The exact historical derivation is uncertain; the term is used in modern educational contexts.