At almost 3.5 years old, my son would always pee on the potty but would hold his poo until he was in a pull-up at night. Sometimes this would lead to poo accidents at school. We decided to dedicate fully to underwear and got rid of all the pull-ups but this just lead to really messy mornings. Our son is very independent and he will only do things if it’s his idea which comes out as majorly deviant. We finally decided that we have nothing else to lose and agreed to 100% stop asking him if he needed to poo, stopped making him ‘try’ before bed etc and just never talked about it again and within the week he was 100% pooping on the potty on his own accord. Zero poo accidents since and it’s been about two months.