Thanks for the thoughtful responses.
@epoh, yes, we are thinking of changing schools. He liked his school and not complaining. The reasons for changing school are different. We are hoping that he'll like his new school as well.
@Cricket, we haven't tested DS's IQ as the need didn't arise. On prepping, I have heard from people about parents prepping their kids year after year and also months in advance, I personally don't know how much truth is to that. This was the first time DS took this test and he mentioned that the questions were very different than what he had been exposed to in his school so he had to think. Did his school help in building those skills indirectly, may be, specially true if those skills are required to finish the school work.
CogAT is used in screening for gifted students in our district. With so many kids scoring higher than norm in our area, including my son, I wonder whether the test is actually a good identifier of the kids who are really Gifted. I doubt that there can be so many gifted kids living in a single area.