Hi username,

Dr. Deborah Ruf wrote a book on five levels of giftedness. But for a summary, check out the link:

http://www.pagiftededucation.info/documents/RufEstimatesofLevelsofGiftedness.pdf

I don't know much about test numbers... but as far as if your child qualifies for "differentiate curriculum" will likely depend on your state and school district's policy.

Hope this helps....
Mag