Usage patterns
学年が上がるto move up to the next school year/grade
When April comes, students move up to the next grade.
学年で一番になるto be the top student in one's grade
She became the top student in her grade.
学年が違うto be in a different grade/school year
He's in a different grade from me, so I haven't talked to him much.
学年ごとに分けるto divide/group by grade level
The students were seated in groups divided by grade level.