A non-explosive, homemade volcano model can make a fine school project. You can fashion the model to look like a specific volcano or make it a generic volcano. The easiest way to make one is with a little old-fashioned papier-mache over a frame made out of cardboard or hardware cloth. Using hardware cloth will make for a sturdier model.
Making a Volcano Model
Start by creating a frame for your model. Either cut and tape together pieces of cardboard to create your basic, volcano/mountain shape or get hardware cloth (or other wire mesh). If your use cardboard, you'll need to cut several triangles and tape them together to make a sort of prism-cone but without a point on top. You can also try making a cardboard cone by bending the cardboard. For something sturdier, use hardware cloth. Hardware cloth is a type of metal mesh, which looks like a grid. A cheap grade is sufficient. Cut the hardware cloth into a cone shape then cut off the point. Bend the cloth around and either solder the edges together to make a tip-less cone or tie the edges together at several points using wire ties.
Now that you have a base for your volcano, cover it with papier-mache. All you need is newspaper strips and papier-mache glue. While layering on the newspaper, you can build up places to make the outer covering rough, more like natural rock, instead of smooth. So let the papier-mache lay thicker in places, creating rocky ledges and trenches down the sides where lava might have flowed. Look at pictures of actual volcanoes for ideas.
Once the papier-mache has dried, paint the volcano to look like natural rock. Again, reference a photograph. Perhaps paint the volcano in an active state with red-hot lava flowing down the sides. For added details, you can glue on miniature shrubs and trees along the base. (You can find those things at hobby and craft stores.) Air ferns also work well for adding some greenery to your volcano.