If anyone is curious how this turned out (finished today)...
I went with pre-gens as with only 10 days, I wanted to jump in playing ASAP. I spent virtually no time discussing rules, but a quick 5 minute overview of RPGs followed by an hour of having the kids work on their character history, personality, how they knew the other characters, etc. I basically treated it as a creative writing/story telling exercise. As you might expect, some kids came up with fabulous characters, while others were reluctant to dive in. This was fine however, as I considered the character development a work in progress.
I chose Tomb of Annihilation as the setting, as I had some ideas how I could make it work with two groups at "the same time.". They started in one large group (about 15 kids) getting the story overview from the PCs benefactor, describing the death curse, establishing why their characters cared, and so forth. That took the second hour of the first day.
After that, they split into two parties (each getting an hour of playtime a day), with each heading to Port Nyazaru in search of leads to the lost city of Omu. While one group played, the other worked in a packet that I put together. This is where they would learn about some of the mechanics, and have a chance to create some of their own material. The packet started with a scavenger hunt, covering the PHB (what does advantage mean, what does 2d6 mean, what would you check if you want to climb something, etc.).
The rest of the packet had them creating a master villain, creating an NPC, creating a trap, creating a new monster by reskinning an existing one, a mapping tutorial, followed by creating their own small mini-dungeon. Each day, before playing, I would check in with the entire class, hearing ideas, helping them with ways to tie things together into one cohesive mini-adventure, etc. By day 10, they had lost some of their luster, but I think I got about 7-8 really productive days from them. I also tried to use some of their ideas when I was working with the opposite group.
Back to the adventure, they spent a couple of class days in Nyanzaru, giving them an initial encounter, finding a guide, and so forth. They then spent a couple more days exploring the jungles of Chult, searching for Omu, going on side quests, and so forth.
For our final week, each group spent a few days in Omu, finding the puzzle cubes in some of the shrines. They really enjoyed some of the puzzle based encounters in the shrines (and they were amazingly good at solving them.) They wound up finding 4 of the cubes (which I considered enough given the time crunch).
On the final day, today, the groups came together in the Temple of the Nine Gods, where I created a final showdown loosely based on the actual adventure, where they faced down the boss, returned the cubes, and cured the death curse.
On the killing blow (a rogue using True Strike to send an arrow piercing the glowing life core of the master villain), the entire class went nuts, a mere 30-40 seconds before the final bell.
Ultimately, the class really hit on what I love about the game. We have limited funds but I was still able to use the Basic Rules and books checked out from the library to give them just enough resources. The rest was all them.
