How should I prepare for an overnight school trip or excursion?

The core of the anxiety is difficulty forming an outlook and the change in environment and daily rhythm. Convey the schedule, place, room, bathing, and meals concretely and early, with photos or an itinerary. Visiting the site beforehand, preparing belongings and steps together, deciding on a signal for trouble and a teacher to rely on, and sharing medication, meals, and sensory accommodations with the school let them go with reassurance. Rather than forcing full participation, design "in what form, and to what parts, they will participate" together with the child and school.