Yes 5 year olds and even 11 year olds and other older and younger kids are going to school now wearing diapers.
It is true that many 11 year olds and other kids are going to school in diapers and not being potty trained.
A friend of mine is a teacher in elementary school and he said that he has seen 11 year olds, 12 year olds, 13 year olds, 8 year olds, 5 year olds and 6 year olds wearing diapers to school and are not potty trained.
Some of the kids that wear diapers may even be wearing them without the staff of the school noticing.
Kids are getting potty trained later and later these days and having a child wear diapers to school is a good thing though as they won't need to use the toilet.
They can focus more on their school work and some kids won't need a diaper change until they get home as older kids can hold their pee and poop in longer.