Hi P.!
Both my boys did the same thing. The Preschool schedule can really help kids with alot of things.
I had read (somewhere) that this "poo-poo problem" is more common than mom's realize. You have a small person sitting on the toilet for the first time......where does all that poop go? What if I fall in? These are questions that are very real to them, and in turn, make it extremely scary for kids to go.
After I had read that, I took the pressure off of my son, and stopped trying to get him on the potty.
I told him, "I know you're afraid of pooping in the potty, so if you need a pull-up, just let me know. But, if you want to try the potty again, Mommy will go with you and hold you so you're not scared."
He began pooping in the toilet like the next day! My youngest boy, too. Weird! All I had to do was tell them that I understand their fears, and that's all they needed to hear.
Patience & no anger is the key, as a mom. So hang in there! Soon enough he'll be going in the potty. Starting Pre-school will help his little "body clock".
Good Luck, P.!
:o) N.