I think SPD can affect training and potty time in general. DS1 is just over 3 and a sensory seeker. When DS1 started potty training (he was about 2 then) there were many times he withheld and we had to be more forceful that I'd like trying to get him to sit and or go. He is still on a routine where we have to tell him to go every 1.5-2 hours (he is just over 3 now) because he usually does not recognize he needs to go until he almost or actually has an accident. He is still in pullups for nap and night, and sometimes does not want to get out of the soggy mess when it's time to change. He still has trouble focusing sometimes on actually going and instead has a meltdown over being told to potty or does sensory seeking things (playing in the toilet water, unraveling the toilet paper, yanking the toilet paper holder from the wall, banging the toilet tank lid and seat, etc.) I am still trying to figure this one out- giving him input while he is on the potty is difficult, needs creativity, and this whole process can be so frustrating trying to tailor the approach to your child's specific needs. Best of luck to you.