My daughter picked up a bad study habit when she was in elementary school. She didn't need to study but still got all A's and awards. We took her out from the private school of 6 years and sent her to the GATE program in a public school. She got overwhlemed at first since her study habit wouldn't fulfil the requirements of the more vigorous program. She finally manage to change her habit. During these two years of training in the middle school, she's now very capable to excel in the pre-IB program in her HS.
Make sure a good study habit is vital for all gifted children. It's from my own experience. Good luck! Gifted children are fun and rewarding if you do the things right for them.
