Limit user access to post on pages, blogs, etc.


I am a total newb brand new user of Elgg... I am using it for a project that I am working on with my 8th grade students. Ultiamtely, I want them to be able to login, upload PDF files + paste the actual content of the file into a blog COMMENT. Those blog comments would then be rated (1-5 stars) and commented on by other student users.

I have figured out the file upload, the star rating system, etc. BUT I cannot figure out how to limit users so that they cannot post NEW blog pages, etc.

Am I missing setting options to limit users (And possibly groups, although I have disabled groups...) I am running 1.8 and I have not seen any plugin options that would allow me to set permissions for users OR groups of users...