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lower grades of primary school (first, second, and sometimes third grades)
低学年の児童は、まだ親の助けが必要です。
Children in the lower grades still need their parents' help.
この本は低学年向けです。
This book is for lower-grade students.
彼は今年、低学年の担任になりました。
This year, he became the homeroom teacher for the lower grades.