Yeah, something like the gentlemen above say. If you set it to privte, no-one but contributors/collaborators will be able to download edit whatnot (there are endless possibilities - pplay around with them).
One caveat: if you do NOT want Google to include your models to GE, make sure that the "this model is real and GE ready" (or what) box is NOT checked.
Although... I believe that those kids would definitely deserve some kind of encouragement, incentives and "real" credits. Why not the whole town/neighbourhood know about their talents and efforts? This is also always encouraging for others (and they won't be spending their time on dope on the streets at least).
But of course, you know what you are doing and I don't want to interfere...
Next week I am starting with a secondary school special afternoon course with kids in my old school (I graduated from). This is something you would call a middle school and high school in the US I think. I am looking forward to what I can achieve with them and I will definitely leave it for them to decide what they want to go public and what to keep private even though we'll be using the 3D Warehouse.