There are bad seeds in every crowd... hard to avoid, but simpler to just ignore. On our 4-day Wonder cruise last month, there were certainly a fair share of misbehaving kids, but they were outnumbered by the good kids maybe 3 to 1.
I got a good perspective on the situation since I have a 17 year old brother (going on 18 in 2 months, so he'll be hanging with the "old folks" next year!) and a 13-year old steppdaughter... they both gave me different views on the teen groups. Nothing horrible, but it's interesting to get the opinions from the two ages.