Designing a simple web application

I'm working on a web application for school, currently being at the point of designing the system. My application will have users with different roles: Admin,Student,Teacher,Parent,Principal etc. They will all have most of the properties in common (each will have a login name, a password and so on), but they will have slightly different behaviour(teachers will be able to assign marks, students to see their timetable, the principal will be able to generate some charts and so on). I want to design the entities as elegant as possible( I looked on some design patterns, but maybe I'm missing something). Using an interface User and some classes implementing the interface doesn't seem like a good option from my point of view. Some guidance would be really helpful.