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In the classroom, we strive to have reliable, consistent instruments to measure student achievement. Assessments must be free of bias. A coefficient of 0 means no reliability, and 1.0 means perfect reliability. Generally, if a test's reliability is above.80, it is said to have very good reliability.

Validity refers to the accuracy of an assessment -- whether or not it measures what it is supposed to measure. Even if a test is reliable, it may not provide a valid measure. Since teachers, parents, and school districts make decisions about students based on assessments, the validity inferred from them is essential.

All this talk about validity and reliability doesn't mean you need to conduct statistical analyses on your classroom quizzes. (Although you may, on occasion, want to ask one of your peers to verify the content validity of your major assessments.). However, you should be aware of the basic tenets of validity as you construct your classroom assessments.

Imagine a school district is looking for an assessment instrument to measure reading ability. They have narrowed the selection to two possibilities. Test A provides data indicating high validity, but there is no information about its reliability. Which test would you recommend?

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Reliability refers to a kind of assessment that shed lights on the results. To validate the reliability, when the test is employed/ administrated to test takers for the period of time and the test is re-employed/ administrated, the results must be the same.
Validity is defined as a process that measure the accuracy of the test. The main concept of validity is known as "it measures what it is supposed to measure.