"Students walk to the school."
Translation:학생들이 학교로 걸어요.
And, as Sam points out below, either translation could be correct depending on the context and focus. Also, the topic particle 은 could be used, if for instance, we were comparing. The professors drive to the school. The students은 walk to the school. They aren't allowed to have cars on campus.
학생들이 학교로 걸어가요. (O) : focusing on the destination and how they go like by walking. 학생들이 학교에 가요. (O) : it's like you are seeing students going to school 학생들이 학교로 가요. (O) : focusing on "the destination" 학생들이 학교에 걸어가요. (O) : focusing on how they go "by walking"
I seem to remember flagging that sentence, since 학교에 should be accepted. "Students walk toward the school" would probably be a better example sentence for the translation given.