Experts suggest that intelligence has a minimum of two components: 1) the ability to adapt to the environment and 2) the ability to learn from previous experience. Most likely, intelligence has more than two components and more elaborate theories are evolving. No matter the components, intelligence is thought to be a combination of environmental influences and genetics. Most professionals believe that each of us has an inherited intellectual capacity, but whether or not we reach it depends on the resources in our environment, as well as our own efforts to learn and utilize our intellectual skills.
When evaluating a young person, a clinician who administers intelligence tests is looking for patterns of behavior or responses that are consistent with the criteria for ADHD. Individuals with ADHD often perform at a lower level on intelligence tests than those without ADHD, because these tests require sustained mental effort. In addition, as previously mentioned, the structure of most intelligence tests can limit the success of a child with ADHD. Many tests do not allow the examiner to repeat instructions or modify administration rules to accommodate the special needs of individuals who may not have attended to the directions properly or who have a hard time sitting still for testing. Experienced professionals are aware of this tendency and combine the results of these tests (if they are used at all) with the results of others to obtain a more accurate assessment regarding intellectual functioning.
The Weschler Intelligence Scale for Children (WISC)
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The Weschler Intelligence Scale for Children (WISC), originally developed in 1949, is probably the most common intelligence test currently in use. It has been revised since that time, and a Preschool version of the test has also been developed (the WPPSI). Each Weschler test evaluates the subject in two areas: Verbal skills and Performance skills. Scores in both of these areas are used to arrive at a Combined Score (the so-called IQ score), which can be used to compare an individual to others (the average IQ score is 100). These tests assess factual knowledge, spatial skills, logical thinking and mathematical abilities. The WISC is designed for use with children between 6 and 16 years of age.
This test evaluates a subject's knowledge of vocabulary, comprehension (i.e., understanding language) skills, and visual pattern recognition. Stanford-Binet scores allow testers to determine at what age a typical student could answer a specific question. People performing at the level of the average person of their age would have an IQ score of 100.
These tests are designed to measure a child's current level of functioning with regard to specific school subjects, such as reading, oral language, written language, and math. Intelligence may play a role in completing these tests, but it is not directly measured by achievement tests.
Children with ADHD who score poorly on IQ tests are often quite bright. Although academic tests sometimes suffer from the same problems as IQ tests (e.g., adherence to standardized rules) achievement test results often more accurately reflect the true functioning ability of children with ADHD. There is often a typical pattern of performance on achievement tests that can be quite helpful in diagnosing ADHD. Scores on tasks that do not require sustained effort to learn are usually high, and vice versa (scores are low on tasks that require long-term concentration). These tests can also be used to differentiate between difficulties concentrating versus a simple lack of ability in a given area.
The Woodcock-Johnson III is designed to measure general intellectual ability, specific cognitive abilities, scholastic aptitude, oral language, and academic achievement. This test is designed for ages 2 to 90. There are several advantages of this test. First, it is not timed, so there is less pressure to work quickly. Also, it can be used with children who are slow to start, have reading disabilities (i.e., the test is primarily verbal and visual, which reduces errors caused by reading), or who have trouble concentrating for an extended time period (i.e., the test can be taken in different sessions). This test can help pinpoint a student's areas of strength and of concern, their learning style, their aptitude in academic areas, and the presence of visual perceptual difficulties, if any.
Wechsler Individual Achievement Test (WIAT)
The Wechsler Individual Achievement Test is an academic achievement test designed by the same authors who developed the Wechsler IQ tests. Testers can easily make comparisons between the WIAT and Wechsler IQ scales, which allows for the determination of discrepancies (i.e., a child who scores high on achievement but very low on the IQ test) and the presence of learning disabilities. WIAT administration is similar to the WAIS, a benefit that allows testers to easily move from one tool to the other. WIAT test scores can be used to compare a child's current achievement level with what is expected for his or her grade level or age group. All tests, except for the Written Expression subtest, are administered without required time limits, thus allowing students to demonstrate their actual knowledge and skill, rather than simply their speed.
Wide Range Achievement Test (WRAT)
The WRAT is designed to measure reading recognition, spelling, and math computation. There are two versions of the instrument, one for ages 5 through 11, and the other for ages 12 and over. This test may not be the best choice for children from minority groups, because comparison groups (to which scores are compared) may not be reflective of these types of children. Despite it's limitations, the test can be used to compare one person to another with his or her age as a reference point, to determine learning abilities and disabilities, and to assess error patterns that could be helpful in planning specific instructional programs.