G.G.
Boys can take a while to potty train... first, let him accompany Daddy on potty trips as often as possible just to want to be a big boy!
I didn't want to have to retrain from potty chair to toilet, so we started on the toilet. I put my son on the toilet backwards, that is facing the tank and straddling it. He had more control and got used to seeing it go in that way. We put a step stool up because we had elongated toilets which are higher than standard. Put a few cheerios as "tinkle targets" to make it a game.
Once he shows a definate interest, take a long weekend where you have a lot of patience and leave him naked from the waist down- hey, it's warm out and you should be able to explain to the neighbors if he's playing outside! (Don't forget sunscreen!) Give him LOADS to drink to get things going and keep a good watch on him. Once he starts, help him race to the toilet. Do the Pee Pee dance at successes and don't scold when he messes the floor. He'll start to get it and hopefully will be well on his way in three days.
My older son is 11 now and was tough to potty train... some take longer than others and it doesn't show intelligence. (My son has an almost genius IQ, but wasn't fully potty-trained until several months after his third birthday!) Have patience and good luck!!!