My DD who just turned 14 a couple of weeks ago, was 13 at the time of the invite, was invited to a co-ed sleepover. Our answer was the same as some of the above, not just no but HELL NO. One of the other people invited was her boyfriend of about a year. Not a smart idea in our minds. Now, boyfriend, they talk on the phone and at school, that's it. No dates, nothing like that. We just don't approve of it and it won't happen at our house either. Someone mentioned band trips, my DD did go to Charleston last month for a weekend band trip but the rooms were not co-ed and my husband stayed in the room right next to our DD, so we were happy with that.
Heather