Request a "core evaluation" from your public school district. Even if your child attends private school or is homeschooled, the district's education specialist who administers gifted testing is required to test your child in most states.
Hire a gifted education specialist to give your child gifted testing. The fees for such testing can be in the low four figures. However, paying for gifted testing out of pocket usually means you have more control over which tests your child receives, and how quickly gifted testing is administered.
Enroll your child in a university research study. Many children's hospitals and child study centers at research universities have ongoing studies, and many studies include testing IQ, daily life skills, verbal ability and so forth. These tests are free as part of your child's participation in the research study.