def take the seat down to the lowest spot so his feet are flat on the ground. if you have the training wheels that go off center raise them both up a smidge( only a smidge) then raise it little by little till he isnt using them much at all.
balance plays a big part. if he isnt using his legs much (not much gross motor/outside playtime) and sits around playing video games it will take a bit longer.
make sure its small enough( i hate when parents want the kid to “grow into the bike”) dont be a cheapo- get him a bike that fits then deal with the growth spurts later.
my son is the master training wheel remover in our neighborhood. he did some little guys and spends like a few days with them and they are off in no time. i know you wont like to hear this but getting a younger kid/ teenager to do it/ someone he looks up to is better than mom or dad. its a fact unfortunately they want to please strangers more than you..lol when the kid gets off the training wheels he makes h im a number plate for the bike in whatever number they want… kind of like a reward.
on the other hand when we were in fla he tried with my nephew who is NEVER outside doing anything physical and has shit balance (except for his game-boy muscles) he couldnt even ride with the training wheels…so it really depends on the kid too.. he was in 2nd grade and only rode the bike maybe 5 times with the tr wheels on about a yr ago..
good luck..and dont worry it will happen. just dont put pressure on him.. if you want to speak to danny at flemington he can give you some of his top secret pointers if you like….lol