K.O.
I have the exact same problem with my 5-yr old who will be starting kndergarten. What I believe is that he will be just fine we he gets to school. When he is not given the option of mommy or daddy wiping his butt for him. My son, I feel, just does it because he know that I will help him. He has been fully potty trained for sometime and will go pee on his own get himself on the potty and go number 2 then call for me to come in and wipe his butt.
I bought flushable wipes and I stand in there with him and hand him the wipes to clean himself and sometimes I just hand him the wipes tell him he needs to wipe himself , remind him to flush the toilet and wash his hands when finished, then I walk out of the bathroom. It seems to be working. I no longer give in (most of the time anyway) and he does just fine. Honestly, I think it is just because he knows that mommy or daddy are going to do it when he asks. Just be straight forward about him wiping himself. I find that when I am right to the point, tell him what I expect hom to do and leave, it works best.
Good Luck!