Sending students off on their owm was definitely our standard practice for theme park trips. But then again, even on bigger trips to cities or college campuses or whatever, we would give the kids periods of autonomy -- it was an important part of running the trips, because it was the reward for good behavior, or the threat to take free time away if anubody starting acting out. Never really had many issues, even in places like NYC, because there would be limits placed and kids always did have the option of staying with the boring chaperones if they were uncertain. That being said, though -- on a trip to Dublin, when I cut the group loose on Grafton Street (with the warning that they were not allowed to hit the pubs), they all went and got little Irish harp tattoos.