The Meaning of an IQ Test Score

Bell curve
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Your child takes an IQ test and you get the score back. You learn that your child, with an IQ score of 150, falls into the highly gifted range. What does that mean? Before you can understand what it means for a child to be highly gifted (or moderately gifted, or profoundly gifted), you need to understand what IQ scores represent.

Measuring IQ Scores

An IQ score is an Intelligence quotient. This is a measure of intelligence, primarily of a person's reasoning ability. The higher the score, the greater that person's reasoning ability.

If we took everyone's IQ scores and plotted them, we would see them distributed in a normal bell curve. That means that most scores would fall somewhere in the center of that bell curve. The score in the absolute center of the bell curve is 100 and that is where we would expect most scores to fall, or where they will cluster.

As the scores move away from the norm (100), we will find fewer and fewer scores. However, to make the numbers meaningful, we need to be able to measure the variability of the scores. That is the purpose of standard deviations, which is, quite simply, the average distance scores are from the norm. Statisticians determine the standard deviation of data through a specific formula.

Standard Deviations

Once you understand these scores and how they fit in a bell curve, you can better understand the different categories of giftedness. Why is a score between 115 and 130 considered mildly gifted? Why is a score of 131 and 145 highly gifted? The answer lies in the standard deviation of the scatter of IQ scores on the bell curve.

The standard deviation used in many tests, including the Wechsler IQ test, is 15. The majority of test scores (about 70 percent) fall somewhere between one standard deviation below and one standard deviation above 100.

Most scores are somewhere between 85 and 115. Those scores are considered the "average" or normal intelligence range.

The farther the score is from 100, the fewer people we will find with that score. If we move one additional standard deviation below and one additional standard deviation above 100, we will find about 25 percent of the scores falling within those ranges. In other words, people with IQs between 70 and 85 and between 115 and 130 make up about 25 percent of the population.

That leaves only about 5 percent of the population who will have scores somewhere beyond those first two standard deviations away from the norm.

Categories of Giftedness

People often want to lump all gifted children into a single group, assuming that all of these children have the same needs. Nothing could be farther from the truth. A good way to understand the difference in the needs of these different groups of children is to consider how far they are from the norm of 100:

  • Mildly Gifted: 115 to 129
  • Moderately Gifted: 130 to 144
  • Highly Gifted: 145 to 159
  • Exceptionally Gifted: 160 to 179
  • Profoundly Gifted: 180

If you look at the scores for each group, you will notice that each category represents one standard deviation from the norm. To understand the difference one standard deviation can make, consider the scores below 100.

One standard deviation on either side of 100 is within the normal, or average, range. Move down one more standard deviation and you move into the range of moderate intellectual functioning (70 to 84). Children with scores in this range qualify for special academic services. Moving down another standard deviation takes us into the range of moderately retarded (55 to 70).﻿﻿ The farther a child's score is from the norm, the more he will require special academic services.

Now move in the opposite direction of 100. An IQ score up to one standard deviation above 100 is considered normal, or average. Move up one standard deviation and you are in the mildly gifted range. That means that a child with a score of 130 is as different from a child with an IQ of 100 as is the child with an IQ of 70, a score which definitely qualifies a child for special services. Move up one more standard deviation and we move into the range of moderately gifted (130 to 144). The same range on the other side of 100 is the mildly retarded range.

No educator would believe that every child with an IQ anywhere below 70 needs the same academic services that every other child in the range would need. The standard deviations below 100 are meaningful. They are no less meaningful when they are above 100.

Cautions About IQ Scores

IQ testing is not a science. It may seem that way at times, but it's not. Scores from tests are really estimates based on someone's test performance on a particular day. There is always a margin of error. The "actual" score could be higher or it could be a little lower, though it's somewhere within the margin of error.

However, it is also important to note that the score won't change substantially. That is, a child who gets a score of 140 did not get that score because she had a "good day." Some people may tell parents about their children, but that's not true. The highest score a child gets will be the best reflection of the child's IQ (within the margin of error). An average child cannot get a score that high just because she ate a good breakfast and felt good that day.

A Word From Verywell

While IQ tests tend to group children into certain categories, it's important to remember that each child is different. It's also best to keep in mind that IQ scores are not designed to be a predictor of a child's accomplishments,﻿﻿ now or in the future. While you might be excited or disappointed with the results, try to keep them in perspective with your child's overall development and individual learning needs.

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Article Sources

  1. Hessl D, Nguyen DV, Green C, et al. A solution to limitations of cognitive testing in children with intellectual disabilities: the case of fragile X syndrome. J Neurodev Disord. 2009;1(1):33-45. doi:10.1007/s11689-008-9001-8

  2. Stuebing KK, Barth AE, Molfese PJ, Weiss B, Fletcher JM. IQ Is Not Strongly Related to Response to Reading Instruction: A Meta-Analytic Interpretation. Except Child. 2009;76(1):31-51.

Additional Reading

  • Sternberg RJ, Kaufman SB. The Cambridge Handbook of Intelligence. New York, NY: Cambridge University Press; 2011.