Teacher here - in my experience, the pupils are told to stay in groups and are left to go around the parks / resorts themselves. There are specific meeting points around the parks that they 'check-in' with. Some groups of children generally have an teaching assistant with them for most of it where additional needs are identified.I wouldn't leave my own 10-11 year old to walk around a theme park and ride alone though, so not sure how I feel about the thought that teacher's may do this on trips. Had always (naively?) assumed that the reason they take so many volunteer parents on these trips was so that they could split into small groups and maintain supervision :/
Not saying this is right (I do not agree!) but that is the practice.