Setting up an elearning environment including threaded conversations

I am looking for advice on the best way to extend my current WordPress site to include elearning capabilities.

I want to be able to create a course which will have a number of lessons each of which will comprise some initial input for the students – video based – and then a set of questions for them to consider and to discuss. I want to restrict access to people who have registered for the course but I am not looking for a paid solution (I will be offering it to invited people for free).

Looking at various WordPress themes and plugins I have found various options for doing the individual components – user registration, course creation, teaching content, collaboration – but haven’t seen a clear way of providing something that provides all of these in an integrated fashion.

Any advice on whether this is possible / how best to do it would be greatly appreciated.

Many thanks, Graham