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Be Responsible and You'll Be Fine
When in doubt, it's usually better to party on-campus rather than off if you're underage. There was an incident in the fall of 2006 where a big off-campus party got busted by the Meadville police. Lots of underagers were there and they had to go to court. Since then, things have calmed down a bit and people have gotten smarter about throwing parties. If you get caught underage at an on-campus party, a lot of times the campus security will just ask you to leave. If you do get caught drinking underage, the first offense usually isn't that severe. If you get multiple offenses, your parents might be informed and you may be placed on probation, but I think that's a rare occurrence.
In the spring, there's a big weekend called "Springfest" where there's lots of outside activities and usually a concert. It's also usually an entire weekend of drunkeness, with tons of parties held around campus, both inside and outside. Campus security is usually low-key this weekend, and stays out of the way unless something serious happens and they need to intervene.
As for academics, the student body votes on the student-created "Honor Code" every few years. The Honor Code is great because it gives students some flexibility that usually isn't seen at other places. For example, one rule in the Honor Code says that students are allowed to take an exam anywhere in the building in which the exam is proctored (except in restrooms and behind locked doors). I think that the students and faculty really respect the Honor Code and appreciate its uniqueness. However, if students are caught violating the Honor Code, they are brought in front of the Honor Committee (again, a student-run group) and sometimes even in front of the Academic Integrity Board (a panel on which both students and administrators serve). The penalties vary on a case-by-case basis if the student is charged with an Honor Code violation. However, I have heard of very few students getting turned in to the Honor Committee and am not familiar with how severe the punishments can be.