"School" is quite variable.
Weak signal: you only went to class and did OK in them.
Strong signal: you had an internship, or undergrad research experience, or part-time employment as a TA/tutor, or have a completed project to show off, or some kind of non-trivial community/group/club/fraternity leadership.
Really strong signal: you published a paper with someone I know and they recommend you to me.