You've received great advice already.  I'll just add  two things: 
1) You may wish to learn all you can on the subject of 
underachievement, especially:
- how underachievement may develop when there's not a challenge worthy of one's potential, 
- brain changes which may occur, 
- the difficulty in reversing underachievement.
2) You may wish to become familiar with the concept of developing a 
growth mindset.  
If whole grade acceleration is contemplated at some point in the future, you may wish to be aware of the Iowa Acceleration Scale (
IAS) and supporting 
research.