I used the advice of my daycare teacher (who I figured was better at this than me - as she has been doing it for over 15 years). She said no pull-ups at all. Bog boy undies only. At daycare, she took him every 20-30 minutes in the beginning, but now stretches him to 45min- 1 hour between trips.
Don't do away with the big boy undies - they can feel the wetness with those. Try taking him to the toilet more often. Let him put stickers on a chart when he goes to on the toilet sucessfully.
My son, who is 2 years 9 months, has been doing it since mid-october. He's just now getting the hang of it. Don't get discouraged and whatever you do, don't give up.
Also, to make potty clean up easier and less puddly, try buying some rubber pants for over the top of the undies - It still wets the pants, but saves you from cleaning a puddle from the floor.