"scottv95 ": interesting experience because it shows that I was right in my message.
funny too because it shows how girls could be mischievous sometimes.
Even if it was generally not planned at all, it could obviously happen occasionnaly or incidently by a luck of check of Pe teachers or school authorities that some girls came in a corridor or a hallway where they hoped to see the boys already undressed as it was in your case.
It was normal that rumors run through the school so that the girls knew that this was the day of the physicals of the boys,and some thought that it was a good opportunity to try to watch them in underwears if they were lucky !
Anyway your exposure to the view of the girls classmates was very quick since the teachers chased them away quickly... and you were walking, not exposed standing on a scale as if the weigh-in would have been performed in the corridor.
But I am sure that such experiences were rather frequent and sometimes more embarrassing since boys could have been stark naked instead of being in underwears like in your case.
I am sure that when the exam took place in a gym, it could happen also that a door stayed opened giving a view into the gym to any persons, including a group of girls, walking by the door in a corridor because somebody had forgotten to close it, or may be it was possible to have a view on the gym by a window which was not closed that day incidently.
In my opinion, it happened never intentionnally ( not CFMN situations which are fantasy) but incidently , there was so much possibilities...andI am quite sure that the teachers were not checking as well as for girls when thre was a physical examination.