As a result of their responses to test items, children were assigned a mental age ormental
levelreflecting the age at which typical children give those same responses. Although mental
age differentiates between abilities of children, it can be misleading when a 6-year-old and
an 8-year-old, for example, have mental ages 2 years below their actual (chronological) ages.
The younger child would be proportionally further behind peers than the older child.
German psychologist William Stern suggested using the ratio of mental age (MA) to
chronological age (CA) to determine the child’s level of intelligence.Mental Age and the Intelligence Quotient
In adapting Binet’s test for Americans, Lewis Terman developed the Stanford-Binet
Intelligence Scale reporting results as an IQ, intelligence quotient,which is the child’s
mental age divided by his or her chronological age, multiplied by 100; or MA/CA ¥100.
A 10-year-old who answers questions typical of most 12-year-olds has an IQ score of 120.
Another 10-year-old who answers questions typical of an 8-year-old scores 80. With the
development of intelligence tests for adults, the ratio IQ becomes meaningless and has been
replaced by the deviation IQ determined as a result of the standardizing process for a par-
ticular test. For the fifth edition of the Stanford-Binet Intelligence Scale for Adults, the test
has been standardized with a representative sample of test takers up to age 90. Fluid reason-
ing, visual-spatial processing, working memory, and quantitative reasoning seem to peak in
the 30s, whereas knowledge seems to peak in the 50s.
The newest version assesses each of five ability areas, such as knowledge, fluid reason-
ing, and quantitative reasoning, both nonverbally and verbally. By combining these subtest
scores, one IQ score is determined.The Wechsler Intelligence Scales
David Wechsler developed another set of age-based intelligence tests: the Wechsler
Preschool and Primary Scale of Intelligence (WPPSI) for preschool children, the Wechsler
Intelligence Scale for Children (WISC) for ages 6 to 16, and the Wechsler Adult Intelligence
Scale (WAIS) for older adolescents and adults. The latest edition, the WAIS-III, has a verbal
scale including items on comprehension, vocabulary, information, similarities, arithmetic,
and digit span; and a performance scale including items dealing with object assembly, block
design, picture completion, picture arrangement, and digit symbols. Wechsler based his
measures on deviation IQs or how spread out the scores were from the mean of 100 (Figure
15.1). Since intelligence has a bell curve distribution, 68% of the population will have an
IQ between 85 and 115. These test takers are considered to be low normal through high
normal. Test takers who fall two deviations below the mean have a score of 70, typically con-
sidered the borderline for mental retardation,while test takers two standard deviations
above the mean have scores of 130, sometimes considered intellectually gifted, and those
three standard deviations above the mean have scores of 145, sometimes considered
geniuses. The Wechsler tests are judged more helpful for determining the extremes of intel-
ligence at the mentally retarded and the genius level than the Stanford-Binet. They also help
indicate possible learning disabilities when a child’s performance IQ is very different from
his or her verbal score.Mental Retardation
Some people prefer the term cognitively disabledrather than mentally retarded. Degrees
of mental retardation vary from mild to profound. To be considered mentally retarded, an
individual must earn a score at or below 70 on an IQ test, and also show
difficulty adapting in everyday life. Typically, mildly retarded individuals (about 85%) score
between 50 and 70 on IQ tests, are usually able to care for themselves, can care for a home,206 STEP 4. Review the Knowledge You Need to Score High
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