T.N.
Eh, I put pull ups on my newly potty trained boys for first week of preschool which required potty trained kids. They came home dry.
What he's like at home might be different than what he's like at school.
They went to the bathroom (whether they 'had to go' or not) twice in the 3 hour day.
You can express your concerns with the admin, but you're right, he won't be the ONLY freshly trained kid, and accidents WILL happen!
:)