Teachers can change a kids diaper in school, but it's mostly special education teachers and teachers aides that help with changing a kids diapers.
If the kid is in diapers in school and is in a regular class, then they would be sent to the nurses office in some cases or a private area with at teachers aide to get their diaper changed if they need help.
Or if they are capable, they will be provided a private area, like a private lockable bathroom where they can change their diapers and the diapers will be kept discrete in a discrete location.
Normal classroom teachers do not usually change diapers, but instead it mainly comes down to special education teachers and those special education teachers aides.
In school when older kids wear diapers, the ones who change older kids diapers in schools is often special education paraprofessionals, like aides, paras, or 1 on 1 support staff or the special education teacher.
In most school districts, classroom aides or 1 on 1 assistants are the ones who are tasked with changing older kids diapers in schools.
In some classrooms, the special education teacher as well as their aides will rotate the diaper changing responsibility or even share the task of diaper changes on older kids as a team task.
School nurses rarely change older kids diapers, especially now, although if they really need to change the kids diapers and someone else is not available, then the school nurse would likely change the kids diaper.
School nurses mostly handle medical procedures and emergencies and rarely change routine diapers on kids.
But if the need arises, the school nurse may step in if the child also requires any medicalized care or if other staff are not available.
Or if the kid is capable of changing their own diaper and is not disabled, and simply needs diapers for urinary or fecal incontinence, then they are often provided a private and designated place to change their own diapers.
If the student does require routine diapering or restroom assistance, it will often be formally documented in their IEP or Individualized Education Program or a medical 504 plan.
I worked with some kids like 7 and 8 year old boys who were just urinary incontinent and needed diapers and they often wore Luvs size 7 or luvs size 8 or another similar diaper and they would usually change themselves.
But others who were disabled would need help and if the child needed help with putting their diaper on and getting cleaned up properly then I as a teachers aide would help them.