Some schools have plants in their school yard for the children. The holders for these plants can be any size or any shape. The students get to plant trees, and flowers, even veggies. They can use gravel or seashells for the plants also. Plants at any school are great projects for art or science class's.
From the senior class to the kindergarten class planting is a great idea. For the senior class, its great to have them write their names in clay. They can plant a tree or bush for their senior year also in their memory.
For kindergarten its a fun idea to decorate a large plant holder with their hand prints. This can be in clay or on large planter also.