There is something to be said about a Sink-or-Swim approach for these young people. They've received four years of college classes, and presumably, some of those classes should have prepared them for being in a classroom as a leader, but that couldn't be farther from the truth. Thinking back to my first teaching experiences, I realize how presumptuous it is to believe that they are prepared. I wasn't, and neither are they.
I've discovered that, though I give them specific instructions for how to improve, they don't often respond by taking those hints and running with them. And that's where the mentor-teacher comes in. I must have failed when I was in that position, but I see it now: the mentor-teacher - the regular teacher in that classroom, the one giving up authority to allow a college student to take over for an amount of time - that teacher is crucial if the student is ever going to learn and adapt.
Before they ever begin to take over that class, the student is supposed to watch and assist. What are they seeing? Are you a mentor who never has adapted and grown yourself? Are you also flailing around, drowning in the waters of classroom management and organization? I've been in some classes to observe student teachers, and I've had to wonder if the regular teacher had any more control or was able to effectively engage the class him/herself. It's pretty obvious actually.
My message for the mentor teacher is that this is not a vacation for you. If you're just going to sit back and relax while they take over, you've volunteered for an opportunity that is lost on you. Yes, you could develop lessons, prepare materials, and organize things for your return to the classroom (That's what I did.), but first, you must be a positive example for the college student.
How do you do that? For one, you must set some expectations for the student teacher. Let him know explicitly what you expect from him. Hold her accountable for her actions in your classroom. And don't forget that you are there to teach them directly. Being an example is a valuable part of the experience, but you must also teach. How about this? While you are teaching your regular class, if something works, point it out on the spot to the student teacher. Take a moment to ask him why it worked. Mention that it is one of the skills you have developed that causes the class to flow more smoothly and causes students to remain engaged and on task.