Since the beginning of the 20th century, psychologists have been trying to refine their methods of assessing intelligence. Standardized intelligence tests are used to assess the abilities of children, employees, military personnel, convicted criminals and the mentally ill. Defenders of the tests say that they provide genuine insight into an individual's capabilities, while critics say they are much too narrow and potentially dangerous if relied on to classify people.

Pro: Valuable Diagnostic Insight

Psychologists have struggled to define innate intelligence and find ways to measure it that don't rely on learned knowledge, instead measuring mental processing speed, working memory and reasoning ability. IQ assessments contain batteries of "subtests" designed to test these, and by looking at subtest scores, it may be possible to pinpoint areas where a person is having trouble and design helpful interventions.

Pro: Identifying the Gifted

Children with above-average innate intellectual abilities often struggle with boredom and frustration in school, which may turn them off and lead to underachievement and behavioral problems. Using IQ tests, educators can identify children who need more stimulation and are capable of learning faster, and offer them a richer educational experience.

Pro: Provide Valuable Data

By testing hundreds of thousands of people in hundreds of ways and studying the results, psychologists learn a lot about the way the brain works. This has led to valuable insight, as well as to constant efforts to improve the tests.

Pro: They Can Be Fun

When researchers at the Brain and Mind Institute Natural Sciences Center in Canada designed online IQ tests for a study, they expected a couple of thousand responses. Instead, they got over 100,000. Almost everyone enjoys an opportunity to find out more about how his brain works and compare himself to others.

Con: They Can Be Biased

It is very difficult to design a major assessment that is independent of learning and culture. Test designers and experts have struggled with this factor for decades. Although some tests, such as the Cattel Culture-Fair and the Raven progressive matrices, are designed to avoid this by measuring intelligence independently of language ability, many mainstream assessments still favor those who are fluent in the testing language or have a solid foundation of general knowledge.

Con: Labeling Can Be Harmful

When anyone, especially a child, is labeled with a number which is considered an accurate measure of his innate potential, problems may follow. Those labeled "gifted" can develop an unrealistic self-concept that leads them to make less effort or look down on others. Those labeled as learning disabled may suffer from the low expectations of educators and others who believe that an IQ score defines their potential, leading to a lack of stimulation and damaged self-esteem. It has been established that effort is a much better predictor of success than innate ability.

Con: They Fail To Measure Other Important Types of Intelligence

Since the 1980s, more and more educators and psychologists have embraced theories of multiple intelligence: that a person can be gifted musically, intrapersonally or kinetically in ways that are just as important as verbal or mathematical skill. Educators have found that identifying students' strengths in this way and working with them can offer a route to increasing that student's performance in other areas. Educators who define students' abilities by an assessed IQ may be less likely to try, and these other types of intelligence are not easily measured by any test yet devised.

The Bottom Line: One Number Is Never the Whole Story

The Canadian study that involved over 100,000 participants was the largest group cognitive assessment in history. Researchers found that no single score could be established as measuring an individual's overall ability. Using magnetic resonance imaging data, they also found that different tasks activate different areas of the brain and that behavioral and emotional factors such as smoking, playing video games or anxiety affected some scores but not others. There's clearly much more to be learned about the fluid, multidimensional nature of intelligence.