Toilet Training - The Sequel

So, from our last toilet training post, we have persisted in our attempt to toilet train Caleb. For those of you who are curious, not all of Caleb's classmates are toilet trained, although his teacher in school did agree that Caleb is old enough to be trained.
Well, I made a couple of attempts over the last two months to train him. If he resisted too much, I would lay off for a couple of days before asking him again to go diaperless at home. I had two failed attempts, partly coz I wasn't persistent enough. We would try for a day and he would pee into his shorts repeatedly and the next day I would stop. We finally succeeded about 2 or 3 weeks ago in getting him to pee in the potty whenever he had the need to.
I had made up my mind to persist on for more than a day. We tried for one afternoon to get him to pee in the potty. Again he didn't tell me in time and kept peeing into his shorts. That evening, Grandpa and Grandma came to our house to babysit him. With their encouragement, and a few more miscues, he finally got the idea. I continued the training the next day and viola! Our boy was in control of his own pee!
Well, with that out of the way, we had to also get him to do his big business in the potty. He had actually been able to do that previously but somehow the sight of seeing his own poo in the potty just doesn't appeal to him I think. Each time he wants to poo, we'll get him to sit on the potty or on the toilet bowl but he wouldn't sit for more than 10seconds before declaring "Dun Have". But he'll continue to give us the constipated look after that. And he'll end up finally pooing into his diaper when we put it on for him.
Though Caleb's very good without the diaper at home, we let him wear pull up pants when he goes to school or when we go out coz he's not 100% toilet trained yet. We told his teacher in school that we're toilet training him and she tried asking him to go to the toilet in school but he refuses to pee into the toilet bowl in school. I'm kind of confused by his behaviour actually coz when we go out, and although he has got his pull up pants on, he'll ask Daddy to bring him to the toilet when he needs to pee.
So back to his big business, he has had a few miscues actually. We brought him to Ma-Ma's house and let him go diaperless to see if he would pee into the potty in a different environment. He did but when he wanted to poo, he just went ahead and did the deed in his shorts. It was really a messy affair after that coz he soiled his shorts, Ma-Ma's floor and her toilet as well. And he has pooed on our floor at home twice over the past two weeks. He'll say, Mummy I want to poo poo and before I can grab him and run to the toilet... out it all comes. I must say this toilet training business requires a lot of patience. But I guess, we just need to take it one step at a time.