As we were very underhanded in this project, I performed several roles normally executed by different people.

I talked to clients about new features and did extensive testing and technical support, did bug tracking in MS TFS.
It was important that I checked if the system executes the business rules as it was supposed to do, limited by the agreed scope. I liked explaining to non-technical business people (most didn’t know much about technology), what can be done and at what effort/cost, as well as keeping the expectations in an acceptable level.
Another task was explaining the users about occasional issues reported in the technical support, such as infrastructure problems, login difficulties, real bugs, issues not in the scope were not bugs, etc.

There are very well defined user roles such as: teacher, school staff and student. Each has different permissions and can do determined tasks.
The most challenging thing here was developing such a complex system with a team of 6 members.