The only disadvantage is that it requires a computer and internet to bring it into a writers' group, but I intend to show it to the youth of our group, anyway--using saved internet tabs if necessary.
The link above goes to the directory, which offers 'help' on the following subjects, many of which can be used to generate random writing prompts or assists, others of which are just fun:
Dial 1 for Settings
Dial 2 for Characters
Dial 3 for Dramatic Entrances
Dial 4 for Dialogue
Dial 5 to Commiserate
Dial 6 for Verbs
Dial 7 for Calisthenics
Dial 8 to Kill a Character
Dial 9 for Endings
Much of this can (and should) be used on your own; dialing five repeatedly brings up a variety of quotes from famous (and less well-known) writers concerning writers' block--many of them less than sympathetic. 6 will over you a random verb. Keep dialing to cycle through. Dialing 8 will offer an option such as the following for the death of a character: 'Deep-vein thrombosis on a 22 hour flight to Bombay.'
Buttons 1,2,3,4, and 9 can easily be the basis for a writing exercise in-class. Take whatever results you get from the button and write a story based on it. If necessary, you can press the button and copy down the results beforehand, but it would really be best if the writers could bring up their prompts in real time. 7, Calisthenics, is specifically designed as a writing exercise ('Bring these elements together to make a story').
I'd recommend you check it out. Regardless of everything else, just cycling through the offered story-components is fun.