Learn About Standard Scores and What They Mean

Standard Test Scores and Learning Disabilities

Standard Scores. Getty Images Credit: JGI/Jamie Grill

Standard scores are used in norm-referenced assessment to compare one student's performance on a test to the performance of other students her age. Standard scores estimate whether a student's scores are above average, average, or below average compared to peers. They also enable comparison of a student's scores on different types of tests, as in diagnosing learning disabilities.

When parents first become involved in the world of learning disabilities and standardized testing, it's easy to become overwhelmed with all the information. Here are some basic guidelines and terms used by educators who administer and interpret standardized test scores. 

Types of Standardized Test Scores

Common types of standardized test scores used in special education assessment and diagnosis of learning disabilities include:

  • Standard scores: Test developers calculate the statistical average based on the performance of students tested in the norming process of test development. That score is assigned a value. Different performance levels are calculated based on the differences in student scores from the statistical average and are expressed as standard deviations. These standard deviations are used to determine what scores fall within the above average, average, and below average ranges. Standard scores and standard deviations are different for different tests. Many of the commonly used tests, such as the Wechsler Intelligence Scales, have an average score of 100 and a standard deviation of 15.
  • Percentiles: These scores show how a student's performance compares to others tested during test development. A student who scores at the 50th percentile performed at least as well as 50 percent of students his age in the development of the test. A score at the 50th percentile is within the average range.
  • Z-Scores: These scores are scaled on a number line ranging from -4 to 4 with zero being in the middle. On this scale, zero is average. Positive scores are above average, and negative scores are below average.
  • T-Scores: These scores range from 10 to 90 in intervals of 10 points. Fifty is average on this scale.
  • Stanines: The stanine scale is also called the standard nine scale. These scores range from 1 to 9 with 5 being average. Scores below 5 are below average. Scores above 5 are above average.

Some test publishers create their own scales of standard scores. Interpretations of those scales and what they mean are available through your child's examiner.

Gauging Test Performance

This list of common types of standard scores can help you estimate your child's performance on tests using these types of scores. To understand the meaning of other test scores not listed here, your child's special education teacher, counselor, or school psychologist can provide you with specific information on any tests your child takes in school.

Don't let the complexity of the process prevent you from asking questions. If you don't understand or disagree with something, make sure you have a qualified educator explain it to you. You are your child's best advocate, and understanding the minutiae of standardized testing can help you decide what's right for your child.

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