There are three types of assessment: diagnostic, formative, and summative.
Diagnostic assessment takes place before instruction. Its goal is to assess what the students know, what they are struggling with, and what misconceptions they may have. A common example is a course pre-test of knowledge, skills, or orientation to a subject. Diagnostics may also be used to determine what classes are best suited for a student and what sort of support they may need to succeed.
Formative assessment takes place during the instruction. It serves a dual purpose, giving the student feedback on whether they are on the right track, and helping the teacher to better target instruction. An example might be a “clicker” activity, a short quiz with IF-AT cards, or computer based feedback on an activity.
Summative Assessment generally takes place after the instruction is delivered. It’s purpose is to assess what the student has learned. Examples might include a standardized test, a midterm, or a final graded project.