Gifted Issues Discussion homepage Forums Identification, Testing & Assessment IQ scores...please explain.

The materials listing IQs of 170+ for exceptionally gifted are almost certainly referencing older ratio or modified ratio IQ tests, such as the SB-LM. These tests calculated "Mental Age" over "Chronological Age" to yield an "Intelligence Quotient", or "IQ". More modern intelligence tests use a normal distribution curve with a mean of 100 and a standard deviation of either 15 (most common) or 16, but still retain the "IQ" terminology, even though there is no longer any "quotient" calculated.

An IQ of 120 on a modern IQ test with a standard deviation of 15 corresponds to 1.3 SD above the mean, or around the 91st percentile, a somewhat generous definition of giftedness. An IQ of 130 on the same test would be 2 SD out from the mean, or near the 98th percentile, and a score of 145 (the cutoff that the Davidson Young Scholars program uses to define "profoundly gifted") would be 3 SD above the mean, or around the 99.9th percentile. So 140, which is 2 and 2/3 SD above the mean, would be about the 99.6th percentile, and would seem to be a reasonable place to put "exceptionally gifted" - understanding that people are much more than their scores on a single IQ test, and that these tests do a relatively poor job of differentiating in the higher ranges, above 2 SD outside the mean. So you might not see a lot of difference between a child with an IQ of 140 and one at, say, 145, or your might see huge differences. Out-of-level achievement testing on a test with lots of "headroom" in combination with IQ scores is often a more helpful measure of what exactly your child might need at a given time.