My son's district uses both the NNAT and the cogat, so that's also an option. They screen everyone in second grade with the NNAT and those who do well (they select the top 5% in the grade - in my child's school this includes scores below the top 5% nationally) are nominated for GT evaluation, which includes cogat testing. Parents/teachers can also nominate for evaluation regardless of NNAT scores. Kids can qualify with high enough NNAT or cogat scores, plus other criteria. They also identify kids as gifted in math/science (high quantitative cogat score), Language arts/social studies (high verbal score), or both (high overall).
I like this model. Do think this works well?
