B.F.
yes! waiting too long his body just pushes it out itself. Is he having constipation problems? Has he had problems with bowel movements before? Remember some teachers and I have caught a few at it and lived it as a child myself...will tell kids "wait someone else just went and you can wait" forgetting it's a first grade "child" hello and that the teacher herself has a way bigger bladder and bowel system.
I over heard teachers tell kids at my son's school you went a few minutes ago you shouldn't have to go again "no".
I think you need to consider having a meeting with the ol' teach and see if she has certain rules of potty breaks. Also if you are involved with the PTSA/PTA you can question a few moms with their experience as to what the teacher is like and their experience, without telling them about your chidls situation/experience in class...you can leave the conversation with "thanks, I was just wondering she seems nice and I didn't know her" I have found this very valuable in getting to know about a teacher and what others have experienced..I realize they are humans and doing a job I just like to know about them since they get to know my child.
Second I would get in contact with my ped..I have sometimes they have have valuable information on this poop subject. See what snacks you are packing is it something that helps you poop?? also have a talk with your child..ask questions..can you go to the potty when you ask your teacher? see what he says...do you have to wait?? are you not comfortable on the potty's at school?? it's up to you to have open conversation wit him...let him know mom wants to help...does it hurt to poop on the potty?/ (if yes, constipation may be happening)
best wishes