Hi, and welcome. Have you looked at your district's policy for admission into GT programs? is this it?
http://www.gwinnett.k12.ga.us/gcps-edprogweb01.nsf/pages/AcceleratedProgramsandGiftedEducationIf that is your program, it looks like they make the decision of who to test after a referral. You could ask if they take outside test results. If they don't, it doesn't make sense to pay for testing unless there's some other program you think your child could benefit from.
As a general matter, getting straight As does not mean a student is gifted, and not getting straight As doesn't mean a kid is not gifted. a straight A student could be appropriately challenged. Not saying you child is not GT. do you feel like he is not being challenged in school? Do you think the GT program offered would solve any problems you're seeing?
