I had this exact problem with my daughter and the only thing that finally got her to poop in the potty was when I basically threw up my hands and pretended I didn't care. It had become such a power struggle, where she'd either wait until night time with the pull-up on, or she'd sneak off behind a corner or door somewhere if she had to do it during the day. I'd sit with her for over an hour before bedtime, reading every book imaginable numerous times, only to have her poop in the pull up 5 minutes later. I finally decided maybe she wasn't ready and I was driving myself crazy. She'd say, "should we try poop on the potty?" and I'd say, 'no, not tonight,' or 'whatever,' acting like I didn't care if she ever did it after all. Wouldn't you know, that stubborn little stinker started doing it on her own pretty much from that moment forward?!?! Then, I had to NOT do the big potty party and song-n-dance that I had tried before. I just acted like, "oh, that's nice, good job," as if I expected it to happen all along. I'd say, it's worth a try at least--sometimes it's their ultimate statement of control, especially when you get upset over it. Good luck!