A lot of what you will read in books and older articles refers to ratio IQ scores, the old-style scores that you would see on the Stanford Binet L-M.
The newer tests use a different scoring system (deviation scores) which top out around 160. A few tests have extended scoring available for kids that reach the test ceiling.
It's pretty hard to distinguish the higher levels of giftedness using IQ tests because there just aren't enough people at that level in the norming samples. I would call anything above 145 HG+ (highly gifted and up), but people use various labels. Schools use various tests and various cutoffs for their programs. There is no hard and fast definition of gifted.
If you do have your little guy tested, the label will probably be the least useful part of the info you get out of it. Good testing will give you insight into strengths and weaknesses and how your kid thinks and learns. Those are the things that will help you tailor his educational experience.
