We have had a similar problem with our first grader. It happened last year in Kindergarten a number of times and is starting again this year. For him, it was just pee. We did see our pediatrician to rule out medical cause. Once that was ruled out, we concluded that either he was having a hard time asking to go (he has a language disorder) or he was waiting too long to go (either because too distracted because also has AD/HD diagnosis or just anxious).
His special ed teacher tried two things. First, a card he could give to teacher or classroom aide if he was having a hard time with asking. Second, they put a timer on and he had to go to visit the potty whether he said he need to go or not. The second option seemed to work best.
Good luck at the meeting. Those meetings can be nerve wracking.