We tested our DS5 at 4 years, 7 months old due to behavioral issues at preschool. I can't actually remember how I came to the conclusion that he should be tested, but I think it was something along the lines of searching out ADHD information and then stumbling on gifted being mistaken for ADHD.
We got a list of local testers from the Hoagies website, and entertained getting a battery of testing from a gifted center (including neuropsych), but decided to go to an individual LEP who was willing to do piecemeal testing. The IQ test cost $300, but besides IQ score, the LEP also provided her opinion on whether he had ADHD based upon her interaction with DS during the testing (she thought he did not). Admittedly, it's not the full picture, but we didn't want to commit to cost of the full testing in the $2,500 - $3,000 range with him being such a young age. And the IQ score alone did help us realize how much advocacy DS would need going forward.
DS thought IQ testing was fun, the tester had great rapport with him, and the cost was reasonable to us, so there was no downside to the testing from our perspective. But there are plenty of posts on this site about testing not going well, not being representative, etc. I would say that, if your DS is somewhat "difficult", make sure that you choose a tester that knows how to accommodate for that. Good luck with your decision.
