This is the 10350th most frequent Japanese word.
高学年
"高学年" means "upper grades" (typically the older grades in elementary school, such as 5th and 6th grade).
In this sentence, '高学年' is used to refer to students who are in the higher grades, typically in elementary school.
高学年の生徒たちは、新しいクラブ活動を始めました。
The upper-grade students have started a new club activity.
Here, '高学年' denotes the higher grade levels in school, emphasizing their growing responsibilities.
学年が進むにつれて、高学年の責任が増します。
As the grades progress, the responsibilities in the upper grades increase.
In this sentence, '高学年' refers to the state of being in the upper grade levels, focusing on preparation for these grades.