Early Childhood Education

Intelligence Quotient (IQ)


The term intelligence quotient refers to an estimation of one’s cognitive ability or intelligence, and is derived by intelligence testing. An intelligence quotient, or IQ, then, is a number estimating an individual’s global or overall intellectual or cognitive ability. In the early 1900s, a French psychologist, Alfred Binet, first used the term intelligence to “refer to the sum total of the higher mental processes” (Wasserman and Tulsky, 2005, p. 7).

With Theodore Simon, Binet completed the first modern-day intelligence test, the Binet-Simon Scale, in 1905; the purpose was to efficiently and accurately evaluate children’s intellectual abilities. Specifically, the goal was to identify children with mental retardation who would need special educational programming. Subsequently revised and renamed, the Stanford-Binet was the first major test to yield an intelligence quotient, in which mental age is divided by chronological age. The Stanford-Binet has undergone several revisions, and is currently in its fifth revision, extending downward to age 3 (currently published by Riverside Publishing).

The intelligence quotient or IQ was initially based on calculation of mental age, determined by the presumed age level at which certain cognitive tasks are typically accomplished. These early calculations of IQ were based on the following formula (Wasserman and Tulsky, 2005):

Mental age (MA) in months divided by chronological age (CA) in months x 100

For example, a child aged 6 years (72 months) who performed tasks at the 5-year-old level would earn a mental age of 60 months and an IQ of 83, according to the following the formula:

60 divided by 72 = .83 x 100 = 83

From this formula, the practice was established—the average IQ was set at 100. Although the formula is no longer used, 100 is still typically used as the average IQ in most formalized intellectual measures.

By the middle of the twentieth century, the Wechsler scales had surpassed the Stanford-Binet in popularity in the United States. David Wechsler, who had some experience with the early U.S. Army Alpha and Beta cognitive tests for selection and placement of soldiers, published the Wechsler-Bellevue Scale in 1939, followed by several other scales, including scales for school-age children, preschoolers, and adults. All Wechsler scales (published by Psychological Corporation) include a combination of verbal (language-based) tasks and performance (visual and visual-motor) tasks that are combined to generate a full-scale IQ (Wasserman and Tulsky, 2005).


IQ Scores

Wechsler’s scales were among the first to use the deviation IQ, which provides “rankings of performance relative to individuals of the same age group” (Wasserman and Tulsky, 2005, p. 13). In this way, an individual’s performance is expressed as a standard score that shows how far his or her performance is from the typical performance for other individuals of his/her age. For the Wechsler and most other contemporary IQ tests, the population average score is set to 100 and the standard deviation is set to 15. Thus, a child earning an intelligence quotient of 115 exhibits performance better than average for his/her age. About 68 percent of the population scores within one standard deviation on either side of the mean (85-115). Another 13-14 percent score within an additional standard deviation (70-85 and 115-130). Only 2-3 percent of the population scores more than three standard deviations above or below the mean. Interestingly, many American schools use scores falling at the two standard deviation mark as cutoff scores. That is, the typical cutoff for students to be identified as having mental retardation is 70 or below while the typical cutoff for students to identified as intellectually gifted is 130 or above.


Nature of Intelligence

The field of intelligence testing has been controversial since its inception. Theorists have offered various definitions and certainly the nature of the specific tasks included in a given intelligence test reflect the theoretical orientation of the authors. Most current intelligence tests include measures of the following abilities or skills: abstract reasoning, problem solving, verbal facility, mathematical facility, creativity, processing speed, memory, and the ability to learn and store new information (Sattler, 2001). Intelligence and intelligence testing continue to be the focus of much research. Most recent IQ tests tend to yield global scores or composites, essentially an IQ score, but also yield scores on various abilities, such as those listed above. These scores can yield information about an individual’s particular intellectual strengths and weaknesses. Individuals identified with learning disabilities tend to have weaknesses in one or more of these areas and strengths in others.

Despite differences in the way various IQ tests assess intelligence, scores on most IQ tests are highly correlated for most people; in fact, IQ scores correlate more highly with other mental measures than do all other types of psychological measures (Sattler, 2001). Thus, an individual who scores well above the average on one IQ test tends to perform similarly on another IQ test. Also, typically IQ is relatively stable over time. That is, measures of one’s IQ at an early age tend to be highly correlated with measures later in life. Measures of IQ at ages 5 and older tend to be fairly stable, with research yielding correlations of .50 and higher (Sattler, 2001). Note that correlations between .70 and 1.00 are very large; correlations between .50 and .69 are large (Rosenthal, 2001).


Factors Influencing Development of Intelligence

There is an ongoing debate about how much of intelligence is due to heredity versus how much is subject to environmental influences. People do not inherit IQ. They inherit genes that influence the development of their intelligence; about 50 percent of intelligence is due to heredity (Sattler, 2001). Heredity determines the range of a person’s abilities and interacts with environmental factors to determine a person’s intelligence. Studies show that the IQ scores of identical twins (with the same genetic makeup) are more similar than those of fraternal twins (with genetic makeup of brothers/sisters). Studies indicate an increase of about 10-12 IQ points for the identical twin adopted into an enriched environment (Sattler, 2001). Other research indicates considerable change is possible (up to twenty points) in a given child’s IQ scores over time. Access to the following can influence development of intelligence: stimulating and enriching experiences, language-rich environment, adult guidance with problem solving, teaching and reinforcing skills and concepts, medical care, nutrition, social support, safety, stability, parental level of education, and infant birth weight. Evidence indicates that intelligence is more malleable in infants and toddlers, when brain development is very rapid, providing support for the importance of prevention and intervention services for young children with cognitive impairments or in at-risk environments (Lerner, Lowenthal, and Egan, 2003).

IQ tests have been criticized as being culturally biased. However, attempts to be culturally fair in IQ testing date back to the early twentieth century when the U.S. Army developed the Alpha tests for literate candidates and the Beta tests for nonreaders and candidates who did not have a good command of English (Wasserman and Tulsky, 2005). Nonetheless, some still consider IQ tests to be culturally biased because certain ethnic or racial groups tend to perform less well than other groups. Others argue these differences are likely socioeconomically based. To guard against misidentification of individuals (i.e., incorrect identification as mentally retarded), currently in the United States, IQ test scores alone cannot be used to identify mental retardation; measures of adaptive or functional behavior must also be gathered. Another important criticism of IQ tests is that they may not yield educationally meaningful information. That is, while they provide estimates of a child’s cognitive ability compared to same-age peers, they do not give precise information on how best to instruct the child. In other words, these instruments tend to have good diagnostic value but limited treatment utility (Bell and Allen, 2000). IQ tests are most useful for estimating an individual’s range of capabilities and whether or not he or she will be able to achieve educational goals expected of same-age peers; the scores tend to correlate significantly with measures of academic achievement (Sattler, 2001). What IQ scores cannot do is give parents or teachers information that would help them to enhance a child’s learning or development.


Preschool Assessment

Early childhood measures of IQ tend to be somewhat less reliable than measures used with older children. Uneven and rapid brain development, shortened attention span, limited and idiosyncratic language skills, and unfamiliarity with the testing context all contribute to the lower reliability (Sattler, 2001). For very young children, assessment of IQ is challenging; measures of infants tend to assess perceptual and motor skills and to be only weakly correlated with measures taken later in life. Starting at age 12 months, measures tend to be correlated with measures taken later. As might be expected, the measures become more reliable as children get older. The last fifteen years have seen considerable improvement in the psychometric properties of norm-referenced assessment of cognitive abilities of young children (Ford and Dahinten, 2005). Also noteworthy are the recent development of nonverbal tests of intelligence, such as the Leiter International Performance Scale-Revised (Roid and Miller, 1997, Stoelting) and the Universal Nonverbal Intelligence Test (Bracken and McCallum, 1998, Riverside). Developed to assess students with no or limited language skills and/or who do not speak or understand spoken English, these tests are designed to provide fair assessments of cognitive abilities.


Current Practices in IQ Testing

Most IQ tests are individually administered and take an hour or longer to administer. Qualified examiners undergo extensive training, using standardized test procedures. IQ testing is part of most assessment batteries for special education in the United States. In particular, IQ testing may be used in determining if a child meets criteria for mental retardation, intellectual giftedness, learning disabilities, developmental delay, and traumatic brain injury. Following passage of U.S. federal special education legislation in 1975 (Education for All Handicapped Children Act [EHA], Public Law 94-142), the field of IQ testing grew dramatically. IQ testing is less common for preschoolers and students in kindergarten than for students in older grades. Nonetheless, IQ testing may be part of a preschool or early primary student’s assessment battery. U.S. federal legislation passed in 1986 (Education of the Handicapped Children’s Act Amendments, Public Law 99-457) established mandatory early childhood special education services for children from ages 3 to 5; in 1991, services were extended to children from ages birth to three (Early Childhood Amendments to the Individuals with Disabilities Education Act [IDEA], Public Law 102-119). IQ tests can provide useful diagnostic information about a child’s capabilities and relative areas of cognitive strengths and weaknesses and can also help determine appropriate educational programming. Further, the scores can help determine if the child is exhibiting significant developmental delays and may be used as a baseline measure to gauge progress and effectiveness of intervention programs.



The intelligence quotient is an estimate of an individual’s overall intellectual or cognitive abilities. IQ is typically measured via an individually administered IQ test by a trained examiner. Intelligence tends to be heavily influenced by heredity but environmental factors also influence development of IQ. Recent trends in intelligence testing include development of more accurate preschool measures and measures that are more culturally fair. IQ scores are most appropriately used to yield diagnostic information about an individual child’s capabilities relative to peers and, when used in combination with other information about a child, can inform important educational decisions.

Further Readings: Bell, Sherry Mee and William Allen (2000). Review: Bayley Scales of infant development. 2nd edition. Journal of Psychoeducational Assessment 18, 185-195; Bracken, Bruce A., ed. (2000). The psychoeducational assessment of preschool children. 3rd ed. Boston: Allyn and Bacon; Flanagan, Dawn P. and Patti, L. Harrison, eds. (2005). Contemporary intellectual assessment: Theories, tests, and issues. New York: Guilford Press; Ford, Laurie, and V. Susan Dahinten (2005). Use of intelligence tests in the assessment of preschoolers. In Dawn P. Flanagan and Patti L. Harrison, eds., Contemporary intellectual assessment: Theories, tests, and issues. New York: Guilford Press, pp. 487-503; Kamphaus, Randy W. (2001). Clinical assessment of child and adolescent intelligence. 2nd ed. Boston: Allyn and Bacon; Lerner, Janet W., Barbara Lowenthal and Rosemary W. Egan (2003). Preschool children with special needs: Children at risk and children with disabilities. 2nd ed. Boston: Allyn and Bacon; Rosenthal, James A. (2001). Statistics and data interpretation for the helping professions. Belmont, CA: Wadsworth/Thomson Learning; Sattler, Jerome (2001). Assessment of children: Cognitive applications. 4th ed. San Diego: Jerome M. Sattler, Publisher, Inc.; Wasserman, John D., and David S. Tulsky (2005). In Dawn P. Flanagan and Patti L. Harrison, eds., Contemporary intellectual assessment: Theories, tests, and issues. New York: Guilford Press, pp. 3-22; Wechsler, David (1939). The measurement of adult intelligence. Baltimore: Williams and Wilkins.

Sherry Mee Bell