I always recommend starting here:
http://www.hoagiesgifted.org/psychologists.htmHoagies is a WONDERFUL website, and the testers you'll find here have been recommended by parents and educators who care about GT education. They're "vetted," if you will.
If you find a tester not on the list and feel the person is good for GT kids, then please e-mail Carolyn at Hoagies and ask her to add the person to the list. She's grateful for the help, and you will help other parents in your same situation.
Okay, so anyone have any testers in CA they want to recommend?
As for what to tell the child, I wouldn't get into "what do you want to do about school?" with him yet. There are plenty of options, but kids generally fear change. There's no reason to go there yet. Get him tested, consider your options, decide what
you think is best for him under the circumstances. THEN start finding ways to make that work for him. Find out what his fears are and work to address those. But just saying "Do you want to skip a grade?" probably isn't going to be met with joy by very many kids, not even really, really GT ones.