I use Junkbuster at home and at work to block access to adverts and the like. You have the ability to control the access files so they could be tailored to your needs and best of all it's GPL'ed http://www.junkbuster.com/ijb.html It doesn't come with a block file, but I'm sure that schools or the LEA could work together to produce one (and publish it for others to view/use). The main problem with (most of the) commercial versions is that they have secrete lists, which may other motives such as blocking sites of freedom of speech. You should have good reason to block a site (i.e. against access policies) and therefore you will have nothing to hide. Hope this helps, Simon Wood