Building and performing with puppets usually motivates the unmotivated. I am NOT talking paper plate, paper bag, or small handpuppets, I am talking about either Parade Puppets, or Sesame sized puppets. With a little research you can get patterns to get you started. Of course this means they will have to learn how to sew (you will be surprised how that excites them too). If anyone wants more information, contact me off list. I ran a puppetry program in a high school that was (and still is, being taught by a former student) packed to the rafters 75% were boys. They like the performance piece (especially since you are behind a stage), and the quick witted improvisational as well as written aspect of it as well. The sculptural aspect could be paper mache, as well as soft sculpture.
just as a visual reminder, here are some of my students' puppets