The work was left to dry until the next class. It will feel rubbery when dry.
While my usual favorite school tempera paint is Sax Versatemp, we used Blick tempera for this project, and the colors work especially well. The pigments seem to leave a good deal of color in the fabric. Try your favorite brand, but remember: NOT WASHABLE PAINT!
This process can also be done with acrylic paint, but the final product will be stiff, whereas the final product with tempera is quite soft. I have also used this process with fabric dyes to paint a shirt.
I know a number of people do a similar imitation batik process using the blue Elmer's gel glue. I tried it once when we ran out of toothpaste, but we found it very difficult to wash out. I have also experimented, with some success, with using a hardening hair gel as the resist. Don't be afraid to experiment! The bonus is that your classroom will smell minty-fresh while you are using the toothpaste, and that everyone will think it is ridiculously silly to be using toothpaste for art.
I have approached this project using a different theme for the artwork each time, and have SO many more ideas. The possibilities are unlimited. You can view my other posts about this process here, here, here, here, here, and here.
One last thought - I think it would be a great idea (though I haven't done it) to contact a local dentist, especially one that specializes in children's dentistry. You might be able to get them to both donate toothpaste (I buy mine at the dollar store for this project), and display the completed artwork!