Welcome!
I agree with Crisc, you should contact the school first and find out what outside tests they will consider. If they won't accept any, find out when they do in school testing and see if it is possible to have you DS set up over the summer, prior to starting school.
Some schools absolutely refuse to test Kindergarteners, so don't be surprised if you get shot down. The important thing is to keep moving forward. If the school won't offer any kind of help, try the district office, ask for the gifted coordinator or special ed (depending on your state). Keep good notes on conversations and follow up with thank you notes. It may take some time but generally with enough perserverance things get done.
