noun
fifth year of elementary school; fifth grader
Abbreviation of 小学校５年(生). Used in educational contexts, often in speech or casual writing.
うちの子は来年小五になります。
My child will be in fifth grade next year.
小五の算数はだんだん難しくなる。
Fifth-grade math gradually gets harder.
小学校 is the full word for elementary school, while 小五 specifically refers to the fifth year or a fifth grader.
Abbreviation of 小学校５年(生). The reading しょうご follows the on'yomi of the kanji.