It also depends how much fluid they have drunk aswell, if this was after lunch and they had a drink of juice they would want to 'go'
I have the same question margy had - do you mean 45 minutes after the child announced they had to "go", or do you mean your child needs to go to the restroom more often than every 45 minutes all day long?
I don't believe so. I had an accident once in 1st grade while sitting in my chair in the classroom and once in 3rd grade while sitting on the gym floor. Both because a teacher would not allow me to go to the restroom and told me to "just hold it". All children have different amounts of control over this, and so the allowance for this needs to favor those children who can not handle it.
Could you enlarge on your question please,I would not think it reasonable if the child needed to go, children dont follow rules about their bodies needs.