Kids don't do any advanced work if there is no reward for it. For many gifted kids challenge or satisfying curiosity are their own rewards. If they aren't challenged by content or material, then they may develop their own challenges like "How to do the least amount of work and score high enough." or "How to blend in and look/act like everyone else." or "How to do everything perfectly." etc.
Some HG kids seem to begin slower but are really just accumulating a ton of information and ideas and suddenly as their brain starts its serious reorganization around 11 then everything can change. Some percentage of HG kids aren't going to find their way without help and become disaffected, maybe dropping out of school or other challenges.
The typical term for that performance vs. potential mismatch is underachievement.
SENG Underachievement
