last week i used 3 day PT, pretty much by the book (except nights- he is nowhere close to waking dry). by day 4, he was pooping and peeing in the potty- no accidents but lots of reminders. day 5 we went out for the first time- gone for a couple hrs and no accidents. he started preschool on day 6- 2 accidents ?at school, none at home. day 7- one at school, none at home. day 8 (today) pooped in his pants twice at school

?i knew he had to poop this morning but he did not before he left. he was in a really bad mood, acting horrible. dh told the teacher he had to go, be on the lookout. when dh picked him up, she suggested pull-ups. ?i'm kinda devastated

?he is doing so well at home. i put him in a pull-up for nights and he HATES ?it. (I have a 4 month old who isn't sleeping so night training just isn't happening right now!) i can't imagine doing that to him during the day after he's done so well in his underwear. i think it would just feel like a diaper to him.
Re: should i switch from underwear to pull-ups?
Was is just that one day? I wouldn't go back if it were me. It's still so early in the process- there are going to be off days. I would talk to your daycare to see if you could give it another few days.
I wouldn't. I think it's awfully early to worry about 2 poop accidents. Does preschool know how early on it is for him? I wouldn't want to confuse or upset him, esp if he's particularly against pull ups.
I would suggest night training- I think it helps with the training as a whole. We night trained DS when he was 19 months old (it was simple). I think it confuses kids that they have to pee/poop on the potty EXCEPT for nightime. Secondly, I would keep the underwear, he's just adjusting to preschool. If the teacher has issues, put a diaper cover over his underwear- it will protect the floor and his cloths.
I wanted to add when we PT DS our DD was 4 weeks old- really it didnt make it hard because we had a baby (I just wanted to add that since I saw you mentioned that in your post)