I will offer one of my better clay activities: I use this with older elementary and high school. It is based on clay that is fired and glazed, but you can adapt to your materials:
I introduce the lesson on "HEROES...not just a big sandwich" The students will create a bust of a super hero - head to shoulders. Develope a lesson around the concept of a bust and what makes a super hero (physical details that might identify a hero)
clay, utinsils for scoring and digging, 1 buned-out lightbulb per kid, some cellophane to wrap the bulb and paints & brushes.
Shape some of the clay into a rectanglular, solid shape - wide enough for the light bulb to be inserted. Wrap the lightbulb witth cellophane and carefully insert to the top long side of the rectangle solid. Using small patties of clay, carefully cover all of the lightbulb - making sure the seams are closed and secure to the base and the coverage is uniform. By now the bulb is covered and resembles a human bust.
Holding the clay covered bulb, turn upside down and dig out the base to leave an even rim and exposing the base of the bulb. Turn back to right side up and cut at the widest part of the bulb all the way around to remove the top part of the dome of clay (I call this "brain surgery"). With the light bulb exposed on both sides, push from the base to remove the bulb and reattach the dome using scoring tools. This part can get tricky as you use your hands from under as well as the out side to avoid colapsing.
From here the kids add or subtract to make eyes, mouth, ears, horns, a cape ...you name it! I have had wonderful success with this lesson and students often request it!