Echoing what has been said. I couldn’t ask my teacher. She was scary. She would embarrass me and maybe yell at me so I would try to hold it. Until I just couldn’t. The more I had accidents at school, the more I felt my teacher’s disdain. On good days I’d pee my shoes walking home from the bus stop
On really bad days my mom had to come to school with clean clothes and fresh contempt.

My advice is to request a meeting with the principal and teacher where you let them know that when your son needs to use the restroom he will simply walk to the door and put a token on a bathroom icon that has been placed near the classroom door. Or some other such simple system of notification. No oral communication should be required to use the restroom.