Personally, I wouldn't charge an extra fee as I see it as just an unpleasant part of the job. As a parent, I think I would be put off at such a requirement and may think about leaving. However, I do agree that he is ready and the parents are being lazy or soft on him and are not doing their jobs. I would probably approach it more from an educating the parents point...give them info on how to do it and make suggestions (sticker charts with rewards maybe?) and really stress to them how he needs to be fully trained soon as he will start school next year and he will need lots of practice before that time to be able to do it independently and not be embarassed at school by accidents. Then you lay out a plan for them to follow and do the same at daycare. If you want to go the route that Crayola suggested, using time-outs, I would discuss this with the parents first. I know I wouldn't want my child to be punished for pottying accidents and I think many parents would feel the same. I have a friend whose son was not trained until he was almost five...he actually went to JK in pull-ups (I was surprised that they allowed him, but they did). With her she tried many things and he was so stubborn (she is a bit soft, so she probably didn't push hard enough early enough). Finally she used a reward system with little prizes and he was trained within a few days.