Well the project is OVER! In the end everything ran smoothly, although the price of paper probably went up quite a bit. I managed to restrict access to back stage so that there was one point of entry.
I notified the parents that they must notify me if their child will be picked up by anyone except them (ie friends parent or a relative), and each chaperone had a list of who the parents of each child were and who was allowed to pick them up.
There were no feinters (I asked that the students be taken to the toilet 10 minutes before they needed to get ready, then given a glass of water to drink), so that was a bonus, and I had minimal overlap between acts - and no stalling.
For access control, I did laminated wrist straps in a number of colours, to denote which area the wearer was allowed, which contained their name and job. Blue, for example, was a chaperone, red was for the teachers who acted as runners, green was "student preparation" etc.
Each class got 15 minutes outside after their performance, and 10 minutes outside during the longer gap between their performances. We put some snacks etc out there too.
All the runners were on 2-way radios, and I had at least one runner positioned at each point of interest (1 outside, 1 in the dressing room, 1 in the students area of the auditorium and 3 'floating')
I was on cans and 2-way radio throughout the night - thankyou techpro for your "2 way interface" - it works beautifully - so my need to know everything was pretty much satisfied.
I am glad it is over, but it was a good experiance.