my 6 year old girl pooing herself

My 6 year old daughter has a problem, but its not there all the time. she is still pooing herself at times more often than not, she does it in the house as well as school, and im at the end now she is pushing me to the edage. i have tryed rewarding her for going and punishing here for durting herself. she has'nt always done it. she was potty trained at just gone 2 and when she turn 3 she started to poo herself, at first i thought it was attenshion but she has started to hide the fact that she has done it now. i really need some advice on what i can try next to stop her.

[Kevin Kennedy, Ph.D.]

She was trained at quite a young age and it is not unusual in such instances for some regression to occur, though soiling herself at this age is not at all within the norm. The most important thing to do right now is arrange a pediatric appointment for her to rule out any medical concern (e.g., encopresis secondary to impacted bowel). If she is given the OK medically, it's then fine to approach this from as behavioral point of view by (a) a reward system for using the potty, and (b) scheduled times at home and school to sit on the toilet. Avoid a punitive approach.