What is valid measurement? It is an examination or evaluation that is characterized by validity. So what is validity?

The main purpose of any assessment is to help the teacher make correct decisions, and the characteristic essential to make such decisions is validity. If a certain paper-and-pencil test provides correct information about students' mastery of given content and/or skills, the test contains validity, and that test is an appropriate instrument of measurement. Assessment should be thought of also as more than graded tests, quizzes, presentations, projects, and the like. If a teacher wishes to obtain correct information about students' motivation, for example, observation may be the appropriate form of measurement. If the observation yields correct information, the method of observing employed contains validity.

How do you ensure valid measurement through the many assessments that you administer? Note that variety of assessments does not ensure validity.