I was really hard on my youngest when he was almost three and not potty trained, and now that he's older I realize he couldn't - he had a fine motor coordination disorder that caused him not only to have difficulty learning to go in the toilet but also learning to wipe. I'm sorry I pushed him so hard now, because in retrospect what he needed was patience and kindness. The little tyke really was trying, but he was my third and I "knew" he could do it and just wouldn't since the other two were competent in the bathroom long before then.
I say this because you commented that he has "some coordination issues". That rings a bell. So ... as gross as it is, and as much as you are ready for this, too, to pass, please consider the thought that there may be something organic going on that is keeping him from doing what he ought to be able to do.
