I'm sorry that your son is having such a hard time. My younger dd's scores were not quite as high as your ds' and she has much lower WMI and PSI thus making the FSIQ lower than the GAI by quite a bit, but some of what you are experiencing sounds a lot like her situation.
She, too, didn't perform nearly as well on the CogAT as the WISC and we were told by both the school counselor and her classroom teacher that WISC scores above the 99th percentile were due to "good guessing." Her classroom performance wasn't poor, but she wasn't a super high achiever and her MAPS scores fluctuated up and down wildly. The times they were high were also attributed to good guessing by the school. She, too, wasn't gifted in their estimation and she, too, wasn't doing well emotionally. She was lonely and her self image was poor.
Have you tried pushing for acceleration at a higher level than the school? I wound up kicking my requests (demands) up to the district GT coordinator. She also didn't feel that IQ scores were equivalent to the CogAT and felt that the CogAT was a better indicator of who was gifted but was willing to convene a committee including pyschologists to review dd's scores. The district policy now allows for IQ to be considered in lieu of CogAT and dd was subject accelerated in math last year and has passed the two district tests required to continue with that acceleration in middle school next year.
I would be doing a few things in your instance:
1) Apply to DYS. I'd expect that he has an excellent shot of getting in.
2) Push for acceleration and inclusion in GT programming at a higher level than the school. Ask for a meeting with the GT coordinator from the district.
3) Look at other schooling options if that doesn't work.
Good luck!
