A writer-teacher buddy said her students refused to write in class. That's a tough one -- what would be the answer? Maybe writing WITH them. Or some really simple word play or totally nonsensical creativity. Or utter silence by the tutor as she/he sits and writes, leaving the students to either pick up their pens or walk out -- too provocative, perhaps?
Meanwhile I've enjoyed and benefitted from completing an application for entry in the V&A Inspired by... adult part-time education craft competition. I had to provide evidence of my creative progress on the project (a papier mache piece), a useful angle on the creative process. Hence introducing competitions to your writers as a way to cajole them into writing and completing.