Ds is 4 in September and we've just gone back to pants in the last 3 weeks and something is finally clicking albeit slowly.
We gave up fpr a while for the sake of my sanity and used pull ups ( a real downer for me being a cloth nappy user 
)
He would say he was too busy/didn't feel like going today/didn't want to and the classic "I don't really need to because you can put everything in the washing machine".
Star charts etc didn't cut it.
WE're now using a small jar (baby food size) and some marbles and a big exciting reward (for him).
Knowing he can do it and just chooses not to, means he only gets a marble in the jar if he has dry pants when he gets to the toilet - no accidents/dribbles allowed anymore because we're a year and a half on from our initial attempts now. If his pants are wet he gets a marble taken out and is told calmly why. When the jar is full he gets the prize (which has been sitting on a high shelf with the marbles in full view taunting him 
) He gets 2 marbles at bedtime if he's been dry all day and 2 in the morning if he's had a dry night (rare).
In the last 2/3 days he's started asking to go to the toilet for pretty much the first time in his life, having always been "managed" before.
I have to really bite my tongue if there's an accident after a run of good days, but he was definitely thriving on the negative attention. But I've toned down the positive praise too, because the overenthusiastic "Oh WOW you are a SUCH a CLEVER boy!!!" isn't really true - more manipulative I think - he should just be getting on with it. My HV said he was too clever and was taking us for a ride.
He's now got a a Charlie and Lola DVD, some dominoes and is working towards a frisbee this week.