Sometimes offering a reward is all in the way you say it.
We had a boy that if you told him "If you do this... you'll get a sticker". He would ignore you. If you told him "You'll get a sticker.. if you do this." he would do it. He was only hearing the first phrase and if it was something he didn't want to do he'd ignore the rest.
Experiment a little and see if that helps.
Positive reinforcement does work. There were times when I spanked my own as well because it was the punishment my parents chose and you tend to fall back on the past.
With my oldest, we would take away priveleges. But then it got to the point where I had nothing left to take away.
So we changed it up a bit. He would have to earn TV/Video time and I made little TV tickets for him.
It's all trial and error. Do what works for you. If you see progress, then tell Mom.
