I don't think the filtering options you link to are realistic for public schools. They amount to configuring your browser to not show images, configure a skin which uses a blacklist of 'limited utility', or use a 3rd party proxy that gets no help from Wikipedia.

> Logged-in users can use personal cascading style sheets to display of images selectively (explained below).

> By filtering content locally, either by configuring their web browser (including the possibility to display no images at all), or by setting up a proxy (such as Privoxy) (explained below).

edit: added limited blacklist option