When my son was in second grade, he was tested for what was hoped to be a brand-new G&T program. He scored an overall 98th %ile on the CogAT, but only 72nd on ELA and 90th on the math section of the achievement test they used. He scored in the 20th percentile on Social Studies -- because in a struggling school, second grade social studies was not exactly a priority! Basically, he could only do as well on the achievement test as the material he'd been exposed to.
So I'm with the others, don't worry about the NWEA. If the GT teacher thinks he'll benefit from the GT offerings, then that's super! Hopefully he can keep exploring his love of math.
