single-grade classroom; single-grade class
Refers to a classroom or class composed of students from a single grade level, as opposed to a combined or multi-grade class. Used in educational contexts.
This school has both single-grade and multi-grade classes.
複式学級 is a combined or multi-grade class where students from different grades are taught together, while 単式学級 is a single-grade class.
Compound of 単式 (single-type) and 学級 (class). The term is a straightforward modern educational term with no obscure historical derivation.