When attempting a quiz for a course in which they are not enrolled, the user is presented with the message, "You need to enrol in this course before you can attempt this quiz." There is also a "Continue" button.
The "Continue" button takes the user back to the course home page without enrolling them. Every user thought that this action would enroll them in the course.
Why it matters
For a sighted user this is a relatively quick process, even if they have to perform every step twice. They'll soon learn that "Continue" does not enroll them and search elsewhere for a way to enroll.
Screen reader users do the same thing, but it takes the much, much longer, and causes more frustration.
Add an "Enroll" button; replace the "Continue" button with a "Do not enroll" or "Take me back" link.