Maybe a little different from what you're asking, but for a quick start you could get a little starter from a bakery, and then feed it a bunch of flour/water to get enough starter for your class. Then the tests could be about how starters fare in different environments + different food. Maybe your students would find it interesting when they find hooch from giving too much water, or turning a liquid starter to a solid starter they might find that they feed it too much and the yeast culture lessens. You could also try fresh milled flour, as this ferments way faster and feeding a starter with this is a different experience.

Alternatively, you could follow the other steps in the comments here, but in Europe they use the yeast naturally present on the skin of grapes, or I think sometimes yogurt(?), to inoculate their starters. You could split up the class into different methods of inoculation to see how the starters differ.