> Should that be a story that might in any way be considered "pulp" (involving war, horror, fantasy or science fiction themes, for example) it would be judged a failure.
There's nothing creative about being given an assignment and jumping straight to topics you're familiar with. Where is the challenge? What do you learn? This is why all fanfiction is terrible-- there are no constraints, not even adherence to canon. Making two straight characters plow each other and go about their business as usual isn't creativity, it's pornography.
Creativity comes from being given a medium and a direction and being told to shape something from it within constraints. It's no different from art class and being given a block of grey clay. Rounding the edges off of it and saying "look, I made something we both recognize as a ball" isn't a creative endeavor. It's laziness. Had you hollowed it out, you'd have a container. You couldn't have at least made a lantern?
The point of these dumbass writing exercises is to subvert them. That's where you sharpen your creative edge. "What the fuck is a Yellow Door, anyway? A portal to an outhouse? What happens if someone falls into it? Do they swim through a literal poop chute and surface in the bog of eternal stench known as Scatlanta? What if that city was built inside the lower intestine of a colossal organism? What if it were at risk of being wiped out by a tidal wave of diarrhea? How would we evacuate an entire city through a single Yellow Door?" (pun intended)
Anytime you think you're done, always be asking what else can you do with this. It's how you find new ways to repurpose garbage to make...art.
Start with utter contempt for the subject and chisel away at the obscenity until something palatable surfaces. Now we get to the actual story: a disaster story, exploring the impossible logistics of evacuating a city ahead of a cataclysmic event. If everyone must evacuate through the Door, who deserves to go through first? Would a mercenary band of thugs (the Rear Admirals?) seize it and charge a toll? Are the people even worth saving, or would they bring disease with them and decimate their next host? Should we evacuate the people-- or route the tidal wave itself through the door instead? Would make for a hell of a geyser.
This entire world was fleshed out from a thought exercise equating the assignment to literal shit.
Prisoners (and the poor) are the most creative of any demographic. They aren't given materials, only constraints. They'll make weapons out of mundane objects, paint with their own blood and feces, turn plumbing into communications networks, distill alcohol, braid fabric into rope, invent languages and encryption/obfuscation methods, etc. Constraints don't stop them. They're what drive creativity.
Creativity can't be taught, only channeled.
What were creative writing lessons at school supposed to do? If the answer was to enable me to write adequate fiction, and to gain enjoyment from doing so, then such classes were a complete failure.
> There's nothing creative about being given an assignment and jumping straight to topics you're familiar with.
I am not necessarily familiar with all the topics mentioned... ;-) Nevetheless, the reasoning given at the time was not yours, but simply that these topics don't constitute proper literature and are therefore not valid topics for creative writing assignments. I have no memory of ever hearing anything along the lines of what you have said above.
Come to think of it, the music and art lessons weren't very good either. Any success I have had along those lines (music) has been since leaving school and not involving anything I learned there.