My son had a similar problem, but the difference was that he had not been potty trained for 7 months. My son, who was 3 1/2 years old at the time, had been peeing on the "potty" for about 6 months, but REFUSED to go "poo-poo." He would repeatedly poop in his pants (for 6 MONTHS!!!) and it was extremely frustrating!! I remember many days where I thought I might have a breakdown! I finally realized that he may be doing it for the attention since the arrival of his baby sister. Once I realized this, my new approach was to tempt him with something fun to do if he went poo-poo on the potty. This may sound like a bribe, and it probably is, but the only way he was going to stop seeking negative attention was to give him positive attention. I told him the first time that if he went poo-poo on the potty that we would sit down and eat cookies and milk together, just the two of us. He pooped on the potty that same day. The next time I told him that we would watch his favorite movie. Again, he pooped on the potty and received his reward. Eventually, he didn't need to be rewarded and would do it all on his own.