I had an English essay assignment senior year of high school that I didn't want to do. I looked through my old essays (never used to delete things) and found one that was almost the same prompt, so I thought "screw it" and changed the date/class name and submitted that. I didn't give much thought to it, but every teacher used the same essay plagiarism checker, and my essay got flagged as being previously turned in. The teacher pulled me aside in class and gave me a lecture about plagiarism and why I can't submit other people's work, so I told her to check the name on the original essay because it was mine. Once she realized I had "plagiarized" myself, she let it go but told me I had to redo the assignment anyway because I "can't re-submit old work".
I would argue otherwise. To plagiarize is to use someone else's work without credit to make it look like one's own work. Re-using your own work doesn't fit the definition of plagiarism.
If the teacher is going to basically plagarize the assignment and I've already done it elsewhere to the best of my ability, how the hell am I supposed to do anything other than resubmit the work I'd done for that assignment the first time?
That doesn't make sense to me. Even after reading the below referenced wikipedia section on self plagiarism, it seems a contested topic and kinda ridiculous.