Thanks Leonid!

Couple of follow up questions...

1) Which module/app would I use to set up membership levels? Accounts Manager?

2) Would the solution you propose allow me to also set up a specific user registration flow for each type of user? In the teacher/student example, let's say I want a new "teacher" user to include a list of their diplomas - which is something I would not need the "student" user to include - would this be custom development or something I could do via Navigation app?

p.s. Feel free to point me to the right documentation/links (I went through the "Start Guide" but did find the info I'm looking for).

I think I'm slowly getting it... for question 1), would it be with the "Permissions" app? (Question 2 I still don't know where to begin...)