What I find is that even when a child is fully trained at home that they take longer to get that way at daycare and it is more a mental adjustment than a physical one. The way I explain it to parents is that at home if they say "I have to pee" parent drops everything and goes with child to bathroom. At daycare if they say it they have to leave the toy they are playing with, leave the activity their friends are enjoying and I have to scramble to make it safe before I can take them to the potty such as putting baby in playpen or craft supplies up. They get so engrossed in play they wait too long - hence accident. They have to reach the stage where they want to be dry and in underwear.

I also found it was a control issue at daycare. If I was busy with another child the training child suddenly had to pee. And in underwear you can't take the chance they are lying so you drop everything and give them your attention in the bathroom. With a pullup I can still call their bluff.