It sounds to me that this particular teacher DID say no, and is now realising that it was a wrong choice and she is covering her tracks.
I wouldn't go over old history, however. The aim of the exercise now, is to put something in place to prevent this happening again. Let the teacher save face on this one, you'll never get her to admit to it. This is another reason why I cultivate "spies" in the classroom - I recruit other kids, not necessarily difficult child's friends, who I can rely on to give me a fairly impartial picture.
difficult child needs to know that he can't just use it as an excuse; but the teacher should let him go, I feel, if he simply doesn't get the body signal in time.
Toileting issues can be huge, for difficult children. difficult child 3 would refuse to go at all, at school. Or he would go for bladder, but not bowel. He would wait until he got home, even at the risk of soiling himself.
Another issue - the toilets can sometimes be a place where bullying happens. A child who goes during lesson time may feel safer, than during break time when the bullies are holding court. If this is likely to be happening, he needs to be protected from this, or somehow helped to be safe.
I recall difficult child 3's teacher telling me with some concern that he was asking to go, urgently, sometimes at half hour intervals. She believed him, there was no indication that she felt he was abusing the privilege, but she was concerned that he felt the need so urgently, so frequently, and asked me to have him tested for possible bladder infection.
Since then I've noticed that he does sometimes have to 'go', at short intervals, with little warning. At home I hear him hit the toilet door with his shoulder like a SWAT team on a raid, then it's Niagara Falls for a few minutes, then half an hour later it happens again. He DOES drink a lot of water, which could be a factor.
I can always tell which member of the household is in the toilet, on what I hear (their approach to the door, whether they lock it or not, the sense of urgency or otherwise, and other sound effects). I have found with difficult child 3 that he has certain times of the day when he has these frequency sessions - usually mid-afternoon.
I would go in firmly but gently. Give the teacher some wiggle room, to weasel out of her position. But once you've talked and agreed on future ways to handle this, if she breaks any agreements you make in the future, let her have it.
And I strongly recommend you cultivate some spies in the classroom - find a kid you can rely on as someone to call when difficult child loses the assignment sheets, for example. Find a number of kids. And be like a good journalist - NEVER reveal your sources.
This spy system can also help you from getting egg on your face, if the teacher turns out to be telling you the truth.
It's always good to feel you know, for sure, what has been happening. It saves you from being talked out of your position if it's correct, and it also stops you from making silly mistakes and antagonising people unnecessarily.
Marg