3 months is a huge amount of time in a 2 year olds life. I wouldn’t stress. He’s just not ready for pooping on the potty. Act completely nonchalant when he has accidents so he doesn’t start witholding. Pay attention to his body language and carry him to the bathroom when he shows signs. Make the time in the bathroom fun and low stress. Songs, books, etc. If he doesn’t want to poop in the potty, offer him a pull-up for pooping and then calmly change it together when he’s done. Reward him for telling you he pooped. After a few weeks, you can try the potty again. Don’t push.

My kids are all much much older now but I recall that some kids were allowed at our preschool if the parent agreed to come in the event of an accident.

Anecdotally, I've had a few parents tell me they sent their kid to PreK not being 100% potty trained and their kids somehow rose to the occasion and managed to do what was expected of them. Some kids want to be rule followers and please a new adult. You could just send your little one and see how it goes. The worst that could happen is the program director tells you the program is not a good fit.

It sounds like he is mostly not making the connections yet. So not really "accidents" but not really fully knowing the task. And the hiding is the indicator that something is up. Do you have choices for him--a small potty and a seat (with a step) that goes on the regular one? If not, try the other. Some kids just do not like the way it feels to go without a diaper. Is he still in diapers? If so, you can try a gradual switch from diapers to the potty by allowing him to go in his diaper, but only in the bathroom. Seriously no judgment, just "this is where we poop; it's ok to use your diaper or the potty." Then after he does that successfully for a bit transition to sitting on the potty with a diaper still on, then after a bit transition to sitting on the little potty with a diaper down below, then just the little potty. We did this method with my first and it felt like an eternity, but really was maybe 2 months from start to finish.

You're probably stressed from the urgency of needing him potty trained by the fall. You have time--three months is a LONG time in kid learning. Try not to react with anger when he does it, just move him to the bathroom to get changed. It'll help the association of where to go.

Oh, and I'd give zero credence to his saying he's not afraid. I'm not sure a 2.5 yo can put that association together.

We started potty training my now-2.5 year old in February. He's doing reasonably well with peeing in the potty as long as we require him to go every few hours (he's not great at telling us when he has to go in time to get to the potty). But he has a low success rate with poop - more often than not, he goes in his pants. I know that he knows when he has to go because he'll often crawl under our table or go in a different room to do it. I try to catch him in time when I see those signs but I don't always notice (he's my second so I have another kid to pay attention to...). I know some might say "he's just not ready" but he's starting preK in September and he needs to be fully potty trained by then, so I'm getting nervous - we really need him to be better by then. Other info:
- I've asked him if he's scared of the potty or if it hurts - he says no
- He poops regularly so I don't think it's a constipation issue
- After he's had accidents I've asked him why he didn't tell us he needed to go but he's not able to articulate an answer, and often denies that he pooped his pants.

Grateful for any (kind) tips - this wasn't an issue with our first so I'm at a loss.