"二年级学生的" can be translated into English as "of the second-grade students" or more contextually appropriately as "for second-grade students" (when referring to something intended for them) or simply "second-grade students'" (when indicating possession, though this form might need adjustment based on the specific sentence structure).
For example:
这是给二年级学生的书。(This is a book for second-grade students.)
二年级学生的课程表。(The schedule for second-grade students.)
二年级学生的作业 (Second-grade students' homework)