You're missing opportunity cost. If you're in school full-time, you're not working full-time. That costs the salary you're not making and the experience you're not getting, on top of what you pay for school plus interest (because unless your parents are rich or you're That Counterexample, you're borrowing).

In return, you go to school, which one hopes is worth the cost over the course of the rest of your life, however you measure it (but here, mostly in currency). Which brings us back to this discussion.