Scores on intelligence tests were originally calculated using a formula that involves division. Hence, they were called intelligence quotient, or IQ, scores. Even though we still use the term IQ, intelligence test scores are no longer based on the old formula. Instead, they are determined by comparing a student’s performance on the test with the performance of others in the same age-group. A score of 100 indicates average performance on the test: Students with this score have performed better than half of their age-mates but not as well as the other half. Scores well below 100 indicate below-average performance on the test; scores well above 100 indicate above-average performance.

IQ and School Achievement

Modern intelligence tests have been designed with Binet’s original purpose in mind: to predict how well individual students are likely to perform in the classroom and similar situations. Studies repeatedly show that performance on intelligence tests is correlated with school achievement (N. Brody, 1997; Gustafsson & Undheim, 1996; Sattler, 2001). On average, children with higher IQ scores do better on standardized achievement tests, have higher school grades, and complete more years of education. In other words, IQ scores often do predict school achievement, albeit imprecisely. As a result, intelligence tests are frequently used by school psychologists and other specialists in their efforts to identify students with special educational needs. However, three points about the relationship between intelligence test scores and school achievement are important to note:

  • Intelligence does not necessarily cause achievement; it is simply correlated with it.   Although students with high IQs typically perform well in school, we cannot say conclusively that their high achievement is actually the result of their intelligence. Intelligence probably does play an important role in school achievement, but many other factors—motivation, quality of instruction, family resources, parental support, peer group expectations, and so on—are also involved.
  • The relationship between IQ scores and achievement is an imperfect one, with many exceptions to the rule.   For a variety of reasons, some students with high IQ scores don’t perform well in the classroom, and other students achieve at higher levels than we would predict from their IQ scores alone. Furthermore, IQ tests seem to predict performance on traditional academic tasks better than they predict performance on everyday, real-world tasks or on unusual, multifaceted problems (J. E. Davidson, 2003; Sternberg, Grigorenko, & Kidd, 2005; Wenke & Frensch, 2003).
  • IQ scores have a limited “shelf life.”   IQ scores do a reasonable job of predicting students’ school achievement for a short period—say, for the following year or two. They are less useful in predicting achievement over the long run, especially when they have been obtained in the preschool or early elementary years (Bracken & Walker, 1997).
In fact, the very nature of what intelligence is changes somewhat as students get older (and thus, how it is measured may also change). The longer the time interval between two measures of intelligence, the greater the fluctuation in IQ, especially when initial measures were taken in the early years (Hayslip, 1994; Sattler, 2001). IQ scores and other measures of cognitive ability often increase over time when children are highly motivated, independent learners and when adults provide stimulating activities and a variety of reading materials (Echols, West, Stanovich, & Kehr, 1996; Sameroff, Seifer, Baldwin, & Baldwin, 1993; Stanovich, West, & Harrison, 1995).