exams

I believe we have exams for the same reason we have averages. The whole point is to summarize what you have learned from that certain class into one test or grade. They help you wrap up the whole curriculum and prepare for the next class (if the class you're taking is a prerequisite). Exams also help you to prepare for when you have to take short courses and have to study a whole bunch of stuff you don't know in a short amount of time. Plus it gives the teachers a last chance to torture their students.