Cogat is never the 'best' test.
It is possible for a child not to do well, and still be gifted.
It is all possible for a child not to do well, and not be gifted.

I think the only way you would get a better feel for this is through an individual IQ test. Did the past psychologists administer an IQ test?

The big question isn't whether he is gifted or not, but if school is challenging him or not. What does he need that he is not getting from school, and how can you work to get that?
Tammy