liquids of different density in layers in a tube with solid objects of different densities floating inside http://www.goodsitesforkids.org/density.htm Density Our quick & dirty explanation of this concept on one small branch page. Contains agreat photo of liquids in layers, plus PhET's Density Simulation. Going in Science > Earth Science. http://www.goodsitesforkids.org/density.htm
Bottle Ecosystem, This is the most awesome class idea to teach ecosystems! Its self contained and you can observe the activity for the rest of the year. No mess no fuss and all of this cost about 17 dollars.
Fun Classroom Activities and Experiments to Interest Kids in Growing Plants