Gifted Issues Discussion homepage Forums Identification, Testing & Assessment wisc iv and wisc 5

So, I have been reading the posts about wisc iv and v. I know about the flynn effect. I also saw a post similar to the issue I am having. I wanted further feedback.

When my son was in 4th grade (age 9) I tested him. His GAI was 136. HIs FSIQ was 128. I had him tested this month again - he is now in 6th grade (age 11). His FSIQ is 113. Not sure of his GAI yet. So, he had a drop of 15 points. Any thoughts? He is being diagnosed with ADD inattentive and very mild dyslexia. We did several tests and the WIAT III has great variability (from grade equ 2 to 12).
Fifteen points seems a lot.