@Moxy I think you're stressing about nothing. In all my years of kids at schools I've never had an issue with one of my kids not being able to go to the toilet when they need to. What I think @BigRedV is talking about are specific situations where teachers get to know the kids who look for reasons to leave the classroom rather than genuinely needing to use the toilet. There are often two bells to end lunch and give kids an opportunity to use the toilet. I've seen the kids lined up outside the room and the teacher will usually remind them to go. Most do. It's handled pretty well by teachers.