I am late to the discussion, but agree with those that have pointed to the possibility of a reading and writing disability. His score on the psuedo word decoding and spelling both indicate that he is not proficient with the sound symbol relationship, word patterns and phonics. Thus, he may have tremendous difficulty with the lower level skills of reading: decoding (getting the words off the page). No surprisingly, his comprehension is higher, but it is most likely compromised by inefficiencies with word reading and fluency.
His math skills also indicate a potential difficulty with lower levels of reading. It is very very common for people with dyslexia to have difficulty with rote facts such as math computation. At the same time, they can be brilliant and exceptionally gifted in math problem solving and math applications.
These issues run parallel to scores in the cognitive realm - you mention that his VCI and PRI scores are off the charts, yet his working memory and processing are much lower in comparison. It is the later that can cause bottle necks in reading/decoding/fluency and in math computation. The former goes to his higher level abstract reasoning skills that play into good comprehension and math problem solving.
I would want to dig deeper on the issue of the dyslexia and would request further reading/literacy testing. Your son could be 2-E - someone that would benefit from remedial reading instruction so that his decoding can improve to the level of his thinking. Most often, diagnosticians would use some or all of these tests: CTOPP, GORT, WRMT, TOWRE, TOWL and others. In addition to remediation, he would most likely benefit from extra time, computer with spell check for writing, calculator for math, audio books/ electronic reader for all written material.
These issues are separate from his ability to access high level science and social studies. However, if he cannot access and take meaning from written material because he is inefficient at the word reading level and at written output, it will be difficult for him to learn in a traditional classroom without accommodations. So much of the material is taught via the written word and assessed via writing, that if he indeed has struggles in this area, he may not be able to convey his understanding and knowledge and teachers will underestimate him.
These links may help:
http://www.interdys.org/http://www.ldonline.org/article/Assistive_Technology_Tools%3A_Reading
http://concordspedpac.org/Whichtest.htmBest of luck - you clearly have a very bright child. I think you have to issues to consider:
1. Does my child have an LD that needs to be addressed with instruction, accommodations or both?
2. Is acceleration appropriate?
These are not mutually exclusive. If you say yes to #1, this does not preclude #2. But if your child does have a LD, I urge you to address it so that it does not cause a bottle neck in future years.