What it is
For some courses, a department will let you earn the credit by passing a comprehensive examination instead of sitting through the course. It is meant for students who learned the material another way — a job, self-study, a non-transferable course, prior coursework that fell outside the transfer window — and can demonstrate the full learning outcomes.
Which courses allow it
Not all of them. Introductory and skills-based courses (a first programming course, a language course, a technical fundamentals course, some math) are the usual candidates. Lab courses, studio courses, capstones, and seminar courses generally cannot be challenged because the learning is in the doing. Each department decides and publishes its list.
The process
You get the department's and the Registrar's approval first, pay a challenge-exam fee (typically a fraction of tuition for the course), and take the exam — which may be a written test, a practical demonstration, a portfolio review, or a combination, and is usually pitched at the level of the course's final. Pass, and the credit is posted, often with a grade of "credit" rather than a letter grade (so it does not affect GPA).
When it is worth it
When you genuinely know the material, need the credit to satisfy a prerequisite or a requirement, and want the time and tuition back. It is not worth it as a gamble — a failed challenge exam may go on your record, may not be repeatable, and you will take the course anyway. Look at a course syllabus and an old final honestly before you commit.
Limits
There is a cap on how much credit-by-exam can apply to the degree (combined with AP/CLEP), it does not count toward the residency requirement, and some graduate programs and licensing boards look at how many of your credits were earned by exam. Check if either applies to you.
Talk to the department first
The chair or the course coordinator can tell you whether the course is challengeable, what the exam looks like, what a passing performance requires, and whether, given your background, it is a reasonable bet. That conversation is the most useful step.
Fictional information
UW–Porter Falls is a work of parody. Every office, person, building, phone number and statistic on this page is invented; nothing here describes a real institution or a service you can actually contact.