S.D.
Hi,
I had a similar problem when my son was 3. He'd go potty with the babysitter but never home. First I suggest at home is removing the pull up. It feels liks a pamper and doesnt help. (Especially after one acident, kids do not like that feeling.) Also, try turning pottytraining into a game. Try puttung cheerios or fruit loops in the pot and have your son shoot the cereal. I know it seems odd, but my son loved shooting the cheerios and it also taught him how to aim!