Simple eLearning website?

I’m setting up an on line eLearning course on my website and here’s what I’d like to do:

I have a course that I want to offer. The course consists of 30 lessons. At the end of each lesson is a quiz. I’d like to set up the website so that only a paid member can access the course. When the member first arrives the only lesson he has access to is lesson #1. He can access lesson #1 as many times as he likes until he receives a passing grade (80%) on the quiz at the end. Then the only lesson he can access is lesson #2. Then the cycle repeats itself until he’s completed all the lessons in the course at which time he can no longer access anything but maybe his account information which shows that he passed all the lessons.

I’ve got the WP eMember plugin which limits access to the course material only to those paid members. Now I need a way to limit the member’s access to only those lessons he hasn’t passed yet.

Any suggestions or ideas?