Give each student a block of air-drying, non-toxic clay. Tell the class that their block of clay represents a mountain.
Tell the students to break lots of small pieces off the clay mountain. Explain that this action is like weathering and erosion, and they are the forces of wind and water breaking tiny bits of rock off the mountains.
Show the students how to press the bits of clay together so they form into a flat mass. Explain that this is what happens to the eroded material from the mountain -- as more and more little bits of rock settle in a pile, the pile becomes so heavy that the small rock pieces press together and stick.
Hand out miniature plastic animals and plants to the students. Tell them to press the models into the top of their sedimentary rock blobs. Explain that these represent the bodies of animals and plants that died and ended up lying on the rock piles.
Tell the students to break more pieces off their clay mountains. Have them layer these pieces on top of the blobs with the plastic figures. Tell the students to press the new pieces down so they form a second layer of sedimentary rock.
Collect the sedimentary rock models and store them until they dry. Hand the dry clay back to the students. Remind them that there are fossils inside their sedimentary rocks.
Give each student a paper bag, and tell the class to put their rocks inside the bags. Have the students pound the bags on their desks to break the rocks into pieces. Then tell them to pull out the pieces and look for chunks that contain fossils. Explain that real fossils were once hidden inside thick layers of sedimentary rock as well.