You can also use a large piece of foam. It is light weight and you can carve it into shape. it would also be able to keep afloat on water, to make it look more real.
GOOD LUCK!!

I’m liking the foam idea previously presented. There are a number of ways you could do this, though. You could build it out of anything if your vision is bright enough. But, if you’re taking it to school, you need to keep in mind what you’ll be carrying it through. Keep in mind that clay can be heavy, and if you drop it, you’re screwed. You could take a poster board, draw the outline onto it, and then make pop-up representations. With foam, you could get a nice large block and cut it to shape, or you can build it up. You could get foam and make the base of the island and then get plastic trees and mountains and such to superglue on. Try to pick whatever is least time consuming, has a budget you can handle, and is least likely to get destroyed at school.

i did a presentation for “Treasure Island”, back in the stone age when i was in school. i used paper mache to model the island, forming it over chicken wire and balloons in various stages of inflation. when it dried i painted it to match an ariel picture of an island. as i recall it was a huge success.

Definitely the foam idea. It’s easy to press in a wire mesh pieces over parts of /on the surface, then finish with a concrete patching waterproof compound, this you mix in sand and fix small rocks, twigs etc for a realistic appearence. You could also carve out areas or work around small 4″ pots and even buy yourself a small bonsai tree. There is also a very great product called winterstone, look it up on google search. Awesome. Good luck with the project.

I really like the foam idea too, but if it’s easier to use household items due to time or money you can make an island from newspaper, flour, tape, and water. Ball up pieces of newspaper to make a basic island shape-you should probably do this on a piece or cardboard or wood to have a base for your project. Use tape to keep the newspaper in the shape you like. The newspaper does not need to be crumpled tightly-you just want the surface you end up with to look the way you like. Then mix flour and water together until its the consistency of elmer’s glue. Cut or rip strips of newspaper and dip each in the homemade papier mache mix. Lay strips across the island and repeat until you have at least 4 layers. You may need to let this dry and add more layers if it does not feel solid enough later. Once it feels solid enough to you, you now have a nice, paintable surface that you can decorate and add flora and fauna to to complete it. This is your very basic, at-home, cheap and easy solution!