Welcome!
I generally consider two most frequently encountered reasons for further evaluation:
1. to obtain insight into a presenting problem (e.g., academic or social-emotional challenges, perhaps related to twice exceptionality, asynchrony, or instruction mismatch), in order to inform interventions or accommodations.
2. to obtain access to additional resources (e.g., GT programming, supportive community).
You also should consider that, since he is already identified as GT, there really are no further diagnostic categories to be had, unless he has a second exceptionality (a disability, IOW). Unless distinguishing his level of giftedness will address either of the reasons for testing I've already listed. You may also already have the kind of testing that would fulfill that objective, since I believe your state public school systems typically administer individual cognitive assessments (IQ tests) for GT classification.
Do you have IRL concerns?
