Tracy from The Science Spot has come through once again with a fantastic unit, Playing with Polymers, in which students make four different polymers - Gloop, Boogers, Goobers, and Super Slime.
Tracy does this as part of curriculum, as part of a study on petrochemicals. I did it at the end of the school year, and the one drawback to doing it then is that this activity does require quite a few supplies and pieces of equipment. But, the students LOVE it - I'll take the mess if I can have engaged students right up until school's out!
And, Tracy does make it fairly painless for the teacher; she includes lists of materials (in quantities for 100 students), recipes, set-up instructions and so on. If you keep the materials well-organized and labeled, things will go smoothly. And your students will love you!