Question about Telnet:

Dear Sir or Madam:

I have the following question to ask you:
I would like to restrict my students from telneting and change to another students’ directories. I would not prefer to change their shell to /bin/true. If I do such a thing they cannottelnet, so I would prefer that they could telnet but they could not use the “cd /” command to go to the high-ranking directories or go to their friends’ directories. Thank you so much for your assistance.