Since the beginning of the 20th century, psychologists have been using standardized tests to attempt to measure intelligence. Intelligence tests are designed not to measure what a child knows but their innate cognitive aptitude and ability to learn. Tests include a variety of items, such as verbal questions, math problems, hand-eye coordination tests, and matching and sequencing tasks. It's been demonstrated that the same person may perform differently on different days; if ill or overtired, for example. Most intelligence tests are designed so that a score of 100 is average.

The Stanford-Binet Intelligence Scale

First published in 1905, the Stanford-Binet Intelligence Scale is the oldest standardized intelligence test. It has been revised several times, and the fifth edition was published in 2003. "Routing tests" guide examiners to the correct level of subtests to administer, measuring fluid reasoning, knowledge, quantitative processing, visual-spatial processing and working memory. The test includes both verbal and nonverbal components and takes between 45 and 90 minutes, depending on the number of subtests administered. It can be used to test people between the ages of 2 and 82.

The Woodcock-Johnson Tests of Cognitive Abilities

The Woodcock-Johnson cognitive tests include a battery of 18 assessments that use various tactics, such as pattern matching, story recall, sequencing and memorization, to measure memory and processing skills. Scoring produces a "GIA," or General Intellectual Ability score. Each assessment takes about five minutes, and they are combined in various ways for different diagnostic purposes. Test designers claim that it can accurately measure ability in ages 2 through adulthood.

The Wechsler Intelligence Scale for Children

The Wechsler Intelligence Scale for Children is used on children aged 6 years through 16 years and 11 months; a preschool and primary version for ages 4 through 6 and a half is also available. There are two batteries of subtests: verbal, which measures reasoning, memory, general knowledge and language skills, and performance, which measure sequencing, problem-solving and spatial skills. Scores on the subtests yield verbal comprehension, perceptual reasoning, working memory and processing speed scores. The test, available in paper and computer versions, takes about 90 minutes to complete.

The Kaufman Assessment Battery for Children

The Kaufman Assessment Battery for Children was developed to be culturally neutral, and is often used for children aged 3-18 who are nonverbal, learning disabled or not familiar with the dominant culture. There are 16 subtests in all, but different age groups take different combinations; the youngest subjects take seven. Four scoring scales measure sequential, simultaneous, and mental processing and achievement. The test can take as little as 25 minutes or as long as 70.