Translation:The student is lazy.
는/은 and 이/가 particles don't indicate plural pr singular forms.
는/은 marks the topic of the sentence (E.g., "학생은 게으릅니다" = "regarding the student(s), [she/he/they] is/are lazy.")
가/이 marks the subject directly related to the verb. "학생이 게으릅니다" = "The student(s) is/are lazy."
In this case they're interchangable, but there are other implications in the way they're used. This video should be helpful: