[K12OSN] Internet access restrictions

[John P. Conlon]

We have a Linux typing lab in our school.  The layout is something we 
got stuck with becaue of the way the school was built.  The problem the 
teacher has is that she can't see all screens at once because the 
terminals are placed around the walls of the room.  Because of the grade 
book and such the teacher needs access to the Internet constantly.

Is there a way or does someone have a routine that would require the 
user to enter a password in order for Eth0 to allow an Internet connection?

I know that there is a way to set up users when the password files are 
created but I don't know how to do that nor  get a chance to participate 
in that process so the users are not restricted there.  How would I go 
about altering the user access files after the fact to restrict the 
students access to the Internet?  Can this be done so that the teacher 
could enter a password to give one time access as needed?

Thanks
Pat