Applying for DYS is a good idea if you are looking for support and another perspective. Please note though that you will have to get him a valid IQ test with qualifying scores. The WISC-III was replaced a decade ago by the WISC-IV, which will be replaced soon by the WISC-V. I am not sure how a 150 on WISC-III translates to a current IQ score or whether it should be translated.
Your WIAT-III score of 143 is closed to the minimum threshold of 145 so another option is to use that with a portfolio. It appears that DYS sometimes accepts applicants who have scores that are below the minimum threshold.
