I have posted here before when trying to train my son who is 4 in may. He is now pretty much toilet trained in the house.
Thing is he won't do it at preschool. Wet pants all time. They have pull up on over his pants - he only has one pair of boots whilst we sort out shoes he can wear - has hypermobility and waiting to hear from podiatrist if he needs anything in particular. He dies tell them he needs it but by time he gets there he's done it.