S.S.
I also have a 4 year old boy. He has been holding his pencils, crayons whatever the correct way for over a year now. I have done it by example - showing him how I hold mine or by getting behind him while he sits and help him by putting my fingers over his (which is pretty hard since he is a lefty and I am a righty, but...) and tracing or writing letters with him a few times and then let him do it on his own. Good luck!