Firstly, considering you're underage, ensure you have parental permission to consume any alcohol, in written form, to provide for the party host (and the police if anything bad happens!).
Also, I'm going to give my honest personal opinion, which some may disagree with. I'm totally cool with this, these are just my experiences and I'm only sharing so that others don't make some of the stupid choices I did, alcohol (in large doses) really is bad!!
1. I don't drink much at all now. I had a few drinks on Christmas and New Years (maybe more than a few on New Years...), but I don't drink in many situations. I used to drink at clubs, but stopped because I had a tendency of getting pretty messy and not dancing well at all, haha. I generally consume maybe 4 standard drinks in a month?
2. Yes, I drank under 18. Between 15 and 17 I drank too much. Like, bottle-of-vodka-at-once too much. There was a stage when I was drinking every weekend with my mates. Sometimes not even at a party, just meeting up in a park. Note that I do not condone this at all, looking back it was horrid and I wish I hadn't done it. During year 11, I returned to only drinking at 18ths, but I was still drinking quite a bit at these events. Then during year 12, I cut right back. By the time I was 18 I was drinking minimal amounts.
3. I think I've been pretty fortunate in having no serious ongoing repercussions of my binge drinking. That being said, I'm pretty sure that, yes, it has impacted my academic results, however generally only through over consumption. Between hangovers and skipping classes to sleep in after a night out, I missed a decent chunk of school. It doesn't seem like much because it's only year 9/10, but these are the years that build the foundation for VCE. if I had paid more any attention in my advanced Maths classes back then, I would have done much better in methods in VCE. I also neglected studying to go out, effectively reducing my results. Also, I believe my memory isn't quite as efficient as it used to be, but nothing major.
In sum, I believe it is fine to consume limited amounts of alcohol on occasions, but not regularly, especially when underage. As Russ pointed out, social drinking generally doesn't have any major effects on development. If you're wanting to do it to fit in, just hold a bottle of coke, or an energy drink or something. If you do want to drink, keep it light, and I'd say discuss it with your parents or someone that knows you closely before you make a decision. As long as you don't neglect your studies, you will be fine. Know yourself and know your limits, and (when it comes to alcohol consumption) stay within them!!!