C.R.
There's a great book called Healthy Baby, Healthy Sleep Habits that addresses this issue. I've had it since my child was young...maybe you could browse the sleep problem chapter because it goes by age in the book (I think it's at the back). I know my coworker has the same issue and has developed a chart. Every night her little girl stays in bed she gets a star and hence works towards a goal or a prize. It seems to be working really well for her. Good luck!!