A Laptop cart would probably be your best option. The cart will allow you the portability to bring the computers to other class rooms, rather than being in a static place, offers a place for them to charge when not in use, as well as offers a secure place to lock away the laptops when not in use. In addition to the portability, you don't have to worry as much about the systems, since you can lock them away when they are not in use. Setting up mini PC's would either make it much more difficult to set up to make them portable or would be at risk for more damage if they were left on each and every desk (not that laptops are excluded from rough and uncaring use).