My DD's currency was preschool. We told her preschool wouldn't take her in diapers. She said she was ready to use the toilet a few days before school started. At that point, it was clear that she was physically capable of using the toilet, but disinterested. For instance, she'd go around in underwear all day with no accidents, asking for a diaper when she needed to go.
The preschool room she was in for the summer would, in fact, have taken her in diapers, so they were fine with dealing with the couple of accidents in the first week. She had a sleepover at school later in the summer, and the teacher, never having known her to be diapered, didn't put a diaper on her for overnight. She woke up night-trained.
