The parent must supply the impetus to change, and to help the child feel the need for change. The child who vomits in the dental office will see little need to change, if he succeeds in avoiding treatment and if someone other than he cleans up the mess. The child must make the choice. If your child feels the urgency and is ready to work, then all is going well. They differ and the difference is of great importance.
Bribery is doomed.
Positive reinforcement will work, if approached with the proper attitude.