It boils down to purpose. In 50 Ways To Measure Understanding, I talked about the purpose of assessment:

Assessment is often discussed as though it were a single act—a quiz, test, or score. But its real power comes from clarity of purpose. If you’re wondering what is the purpose of assessment, the answer drives everything—from design to use.

Formative assessment (What Is Formative Assessment?) is designed to inform instruction…

Assessment is generally broken down into types of assessment such as pre-, formative, and summative.

Related Reading

• 50 Ways To Measure Understanding
• The Characteristics Of A Good Assessment