I never thought, when I began teaching, that I'd spend so much time with drama. This isn't the pedestrian kind, where something bad happens and you react, but performances on stage.
Fantasy and science fiction may not be an easy match for stage performances. We tend to think of this genre as relying on special effects a lot. It does tend to, but the truth is that you can put on some great shows with few or even no special effects. If you want some good examples of this in our culture, look at The Twilight Zone or The Outer Limits. These were very effective shows that relied on storytelling, scripts, and good acting. Sure there were a few special effects here and there, but they were nothing any amateur couldn't pull off with a digital video camera and iMovie.
A great way to start with fantasy-based drama are the ancient Greek myths. These stories are by their nature short and exciting. There are several publications where you can get scripts for plays based on Greek myths, and a quick Google search for “Greek Mythology Plays” will give you many leads.
If you can't find a play that you like and you're handy with writing, write the play yourself. There are dozens of plays that lend themselves to scripting easily. Each can be converted into a fifteen or twenty minute play without too much effort. The favorite stories such as “Demeter and Persephone”, “Perseus”, or “Theseus and the Minotaur” can easily be transformed into play. The last two are traveling plays, and the hero's adventure “on the road” provides lots of opportunities for small roles for students.
One suggestion I have is that you should write the play for your class size, putting in a chorus. A chorus (in the classic sense) can serve a few purposes. You can make them into townspeople and have them provide the necessary exposition. The chorus can also have a flexible number of students. Write the parts and then assign them to how many kids you have for the production. As well, since some words should be spoken in unison, the chorus serves as an excellent role for students who are shy or frightened of performing on stage by themselves.
Plays based on Greek mythology are very easy to costume. All you need are shorts, a white tee shirt, and a white sheet. The sheet should be wrapped around the child toga-style and fixed with a few judicious safety pins. Students should go barefoot.
I have found drama of this kind to be very successful, and there's no better way to teach ancient Greek culture than to put a costume on a kid and have him/her act it out. While teachers are under a lot of pressure to teach to specific tests, a play can be a powerful motivator for student learning. As well, it's a perfect way to teach public speaking skills. Instead of having a students get up in front of a class and give a speech, have them put on a play!