School Intranet plugin

Hello

I’m trying to do the following:

-I need to create a school’s site where the students and teacher have access to a private section of the site with their usernames and passwords.

-I need that the teachers be able to post information (like bulletins) and that information could be seen by all the students.

-I need that information to contain dowloadable files, like .pdf’s with the course material.

How can i do that? what options of plugins do i have to do that work?