There are different levels of understanding among these students.
The gap in academic abilities in this class has shrunk.
ーThere are different levels of understanding among these students.
「この生徒たちの間では理解度に差がある」
level of understanding で「理解度」
among these students で「この生徒たちの間で」
ーThe gap in academic abilities in this class has shrunk.
「このクラスの学力の差は縮まってきた」
academic abilities で「学力」
to shrink で「縮む」
ご参考まで!