My sister used to use the reward chart quite effectivly when her ds was younger (& now with her younger2) these days though when he wants something from her or for her to do something for him, like can i go to so & so party or can you give me a lift... she just says no because yesterday (or when ever) I asked you to... or not to.... or you did.... so why should I do ... for you?
Proberbly the later is not appropriate for you 'YET' but now she only has to give any of the 3 of them 'the look' and they behave (well most of the time lol) I used the reward chart for ds for pocket money (jobs & behavour) right up until he was about 14 and it always worked for him.