I have worked for a company, where we had a contract
to wire hundreds of (catholic) schools to high speed
Internet. With some expertise, one can create a system
that cannot be defeated. Sounds to me that the yeshiva,
does not have a professional firewall/internet filtering
solution. It has to be impossible to defeat, else parents
would have the right to sue, if their kids get exposed
to inappropriate things.
The best solution at home, is to install K9 web protection,
which is free. (do a google search for it). As long as
nobody knows the password, the only way to defeat it, is to
reinstall the operating system.