I had a parent of an older teen ask of Bonnaroo, "Is it worth the money? ... Is it safe?" Here's a edited version of what I wrote back.
Is it worth the money? I can say it is for me, but this year will
be my 9th time going, so I may be a little biased. Given the number of bands that you can see over the long weekend, I think it is a good buy. I have kids, so I'm not able to get to as many shows during the year as I used to, Bonnaroo is a great chance to"catch up" for me.
Is it safe? Mostly yes [...] here is what I think the most important consideration is. How mature and responsible do you think your child is? The reason I ask is that 'roo is like most of the world, if you are smart and don't go looking for trouble, trouble will probably pass you by. However, if you are less than smart or actively go looking for trouble, there is plenty of trouble to be found. For the average older teen I'd think the two main dangers are the heat and drink/drugs (and they are related).
Last year was not bad weather wise, but some years 'roo has been brutally hot and sunny. Talking w/ the people in the medical tents, the majority of cases they see are for dehydration, heat exhaustion and heat stroke. This is avoidable if you pay attention, drink LOTS of water (there are free water stations), wear light colored clothes, hang out in the shade when you can, pace yourself.
There are drugs and alcohol at Bonnaroo. Both are easy to get, even for a teenager. Nobody is going to be pressuring your child to take drugs, but there are plenty of people happy to sell them if he's interested. Few people OD on drugs at 'roo (there isn't much "hard" stuff), but Ecstacy ("X" or "Molly") can increase dehydration, which can be a big problem.
Personal violence isn't a problem at Bonnaroo. I don't think I've ever seen a fight there. I'd not worry too much about that.
I really hope I didn't scare you; the VAST majority of people leave Bonnaroo with nothing worse than sore feet, smelly clothes, a little bit of sleep deprivation (shows go until 3am) and a whole lot of great memories. About 80,000 people go to 'roo every year and there are very few problems. I've been to a bunch of fests and Bonnaroo is actually very well run.