Immobilize the step stool with bungee cords
Kate solved the problem of the wandering stepstool!
My son's cheap plastic stepstool was always skittering across the floor when he was trying to get onto his elevated chair at the dining table. (We have the chair up on a Kaboost) It was one of the white ones from Ikea that comes with holes on the sides, so I looped a bungee through the loops and around the base of the Kaboost. Voila! A solid and safe launching pad! It worked so well that I did the same thing with the stepstool in front of the potty. Voila again! He could maneuver himself up and down off of the seat without needing help.