12 laptops in a classroom which are not networked..you know keeping kids off porn sites and only allowing them to access what sites the teacher says they can.
You will have to install these programs on each of the systems.
There are some commercial programs out there as well. If the users are going through a router to access the Internet, you config the router to block addresses.
my school uses something like PHP..... and when we cant go to a site it says BESS CANNOT GO THERE and show a dumb dog that i wish was like Lassie WOULD DIE!!!!!but its not perfect