Can I just post a little (possible) encouragement? DS went to school not toilet trained with wees, though could with poos, as pp are saying. Nothing worked for him, nothing. And I hold my hand up and admit he was Yr 3 before he was completely dry during the day (night time he was dryer much sooner). HE was the one coming out wet, in fact I could smell him most days - even though nobody else could, I was that attuned by the end.
But it did happen.
He did it, himself, in his own time. I suddenly realised that the replacement underwear hadnt been used for a while. A long while. He is now 13, and well well away from it all. He has also since been diagnosed with Aspergers and Dyspraxia, both of which I believe can make it harder for children to learn toileting. (NB I am not saying this is the case for any children being spoken about on this thread, just my DS).
I also do not think he suffered socially at school from it. He did not appear to be ostracised by any of his peers because of it.
But, it does happen, they will get it and more than likely a lot sooner than it did for me. I understand that the majority, if not all, reception classes will have a couple of children who are not reliable. All I would do is make the teacher aware in advance, if at all possible.