noun
first grade of elementary school; first-year elementary school student
Abbreviation of 小学校１年(生). Used in informal school-related contexts to refer to the grade or the student.
うちの子は来年小１になります。
My child will be a first grader next year.
小１の担任をしています。
I'm the homeroom teacher for the first grade.
Full, formal term for a first-year elementary school student. 小１ is the common abbreviation.
Abbreviation of 小学校１年(生) (しょうがっこういちねん(せい)).