Play Clay Recipe

I was asked to make a batch of homemade play clay for my son's 2nd grade class. The recipe is really easy to do with ingredients you should already have at home. It is cooling now and doesn't look like "playdough" at all so hopefully it will turn out the way the teacher intended. I think I will try this at home on a rainy day sometime for some fun with my boys.
Here is the recipe and some pictures of the process and the finished product:

Play Clay Recipe

1 cup cornstarch
2 cups (1 Pound) baking soda
1 1/2 cups cold water

In medium saucepan, stir together, cornstarch and baking soda. Add water all at once and stir until smooth.
Stirring constantly, cook over medium heat until mixture reaches the consistency of slightly dry mashed potatoes. ( Mixture will come to a boil, then start to thicken, first in lumps and then in a thick mass; it should hold its shape.)
Turn out onto a plate and cover with a damp cloth; cool.
When cool enough to handle, knead thoroughly on a cornstarch dusted surface until smooth and pliable.
Store completely cooled clay in a tightly closed zip loc container.