I've had the dream many times. Usually it is also in a classroom that I never had a class in. You usually know all the classroom doors and which are your classes. I'd say 90% of the time, it is my English class I have this dream about and I go in thinking I'm gonna fail since I missed about 6 weeks of classes. Maybe it is because I think now I'm getting older and I'm starting to lose some grammar skills. I start questioning how to spell words, etc. that I always have known how to spell. I also believe it has to do with feelings of "failure" in life or some job or hobby you do that you beat yourself up about.
This dream is also usually accompanied by the "I can't find my locker" or "I can't remember my locker combination" which is followed by remembering the locker combination and marveling that I "still remember it after all these years"
This dream is also usually accompanied by the "I can't find my locker" or "I can't remember my locker combination" which is followed by remembering the locker combination and marveling that I "still remember it after all these years"

Not the panic you were likely feeling, but the... okay no, it's all pretty funny. The paperclips, the paper skirt, the paper you were wearing being the homework you have to turn in... gold! I've definitely had these types of dreams; the scary anxious, unprepared kind of dreams where you've forgotten your homework, or can't find a book for class, or you're naked at the office, etc.
. If you're able to remember what you're dreaming when you wake, I find my dreams can be an interesting insight into the things in my life I'm ignoring and need to pay more attention to.