That's surprising to hear that some schools either won't let their 1st year students go, or discourage them from going. It would make sense if it wasn't possible to reschedule something, but other than that, it doesn't make sense to me why they would care if they went.
Lots of people went to conferences during my first year, and as far as I know, no one ever had trouble rescheduling test/quizzes/assignments. Professors generally were happy for us to go and encouraged it, and were great about rescheduling stuff.
As far as classes go, if you really learn best by hearing the lecture, it might be a little harder for you to miss class (but some schools record lectures, so then it really wouldn't matter if you could just watch them when you got back). Most of the professors at our school put their lecture notes online so you can get the notes if you miss. It really has a lot to do with your learning style and with how comfortable you are missing class. There are some people in my class that hardly ever come to lecture, and they do just fine.
It may be trickier if you have any required attendance classes, but your professor and you may be able to work something out if that were to come up (we only had a few required attendance classes 1st year that were only scheduled once a week or a few times a month, and we could switch lab sections if we were going to be gone on the day our lab section was scheduled).
