How do I train the kids to sleep earlier?

One of my friends simply explained to her then-6-year old (towards the end of last year) that she has to sleep earlier as she will be entering primary school soon and has to adjust to waking up early. Her girl was excited about attending primary school and accepted the change quite readily. To make it more "enticing" for her daughter, she added that it is her "responsibility" to make sure she start getting ready for bed herself. She gets a "star" every time she successfully starts her bedtime routine by herself. But I think every child is different. I've some other friends whose children runs on their own schedule and had not been successful in enforcing an early bedtime.