I usually HATE the idea of using pullups, but in a situation like this, I would say....put one on this child. Not a diaper though, at least a pullup gives the child the sense that they are taking a step forward...I a firm on, NO DIAPER once the training begins, this child needs to know NO MORE IN PANTS! putting a diaper on part of the time and undies the rest is way too confusing and defeats the purpose of training! Given this child is still pooping in pants, they are not trained and need to be covered by more than undies. Underwear are a privilage and must be earned, if this child is filling his/her drawers each day with poop, they are not earning the right to have undies. I would definitely use positive reinforcement when doing well and at that age the expectations are higher, so I would also use some negitive reinforcement for the poops (losing priveledges etc.) When kids are having a hard time training, its not usually their fault as much as it can be the parent, in a situation like this one....it seems the mixed messages between your house and their house have this kid up in confussion. A lot of times I will put the preasure on the parents by informing them, if their child reaches the age of 3.5 or 4yrs tops and is not trained COMPLETELY! I can no longer provide care! you'd be surprised at how fast they will put in a good and solid effort! good luck!