I've told it several ways. This one seemed to work well with kids:
Me: ...So a long long time ago...
Students: How long?
Me: Hrm. When you could still hear Boyz II Men on the radio.
Students: No one listens to radio anymore!
Me: Ugh. Anyways. There was a boy who came to the United States with his family hoping for better opportunities and a better education. After a recommendation from a counselor, he decided to take AP Computer Science in his sophomore year, which back then was in a programming language called Pascal and students worked on Apple IIes with green monochrome monitors and floppy disks.
He did well in the class, usually getting one of the higher scores on quizzes and tests and he was certain he would do well on the AP test. On the AP test, he breezed through the Multiple Choice section and felt confident about his performance, at least until the Free Response Questions section.
The first question in FRQ that he worked on is a function called square root. He thought long and hard about what the question was really asking and about the kind of answer the function was expecting. A satisfactory answer wasn't coming to him as quickly as it previously had in class and in practice tests. As time passed, he began to feel that a solution would elude him. Throughout his academic career he was successful because of his persistence, so he persisted.
About half-an-hour, maybe 45 minutes later, he decided that at the rate he was working, he'd never finish the test. He wasn't one to give up easily, but after some hesitation and indecision, the anxiety about not finishing the test got to him. He finally decided to move on and work on the next question and revisit the first question if he had time later. He turned over the page and looked at the next question and noticed that it said #1. Puzzled, he turned back to the first question he worked for close to an hour to see what was going on. He was shocked that it had no number. Was this a typo? Did College Board make a mistake? Upon further examination, the question that he worked on before wasn't even a question, it was just an example. His heart sank.
He doesn't remember if he completed the test, probably just blocked out the memory. He did get a score of 3 on that test, and the following year he felt it necessary to redeem himself by doing better on an even more challenging test (Computer Science AB), which he did. Eventually, the boy grew up to become a teacher and to tell his students a cautionary tale about the pitfalls of not reading directions carefully on the AP test.
This is a story I tell my students every year about the importance of reading and following directions. It took a little digging, but here it is. With a little annotation, it is pretty self-explanatory. Feel free to share it with your students.