Our children were tested in first grade. They were selected for testing by their teachers, although any parent could request that their child be tested. My son "passed" the test, and was one of 10 kids identified in his class (over 250) as "gifted." I do not know what the test was, nor do I know the cut off. My daughter did very poorly on the exam, which was a shock to her teachers. We had her privately tested, WECHs IQ test (I could have that acronym wrong), and used that to get accepted into a program for the highly gifted (which they both started in 3rd grade).
We are now 5 years into the program, and I will just say that I wish I hadn't been so anxious to get them into a specialized program. Yes, they are learning interesting things, and my quirky kids have been socially accepted (something they were not in traditional school). However, they haven't learned good study skills, and they refuse to do much prep work for any exam because they believe themselves to be "gifted." Sigh.
It's a hard decision to make. In retrospect, I think I may have been better off in a regular, run of the mill, Minnesota school.