A C206 Instructor Pilot reported that the aircraft's right brake failed on taxi out because the student pilot also aircraft owner; over used the brakes. The aircraft departed the taxiway but no damage resulted.

Narrative

During a taxi on a training flight I noticed that my student was riding the brakes a little bit when leaving the ramp. I commented that overheating of the brakes and overuse is a primary cause of failure. As we turned from Taxiway C to A it felt like my student stopped his brake use. Toward the end of the taxiway he commented that something didn't feel right and called for me to take the controls. When I did I felt left brake pressure but none on the right side at all. With an estimated 8-10 yards left and too much speed I applied full back elevator and what brake pressure I had. The aircraft turned to the left slightly and we departed the end of the taxiway. No damage was done to runway lights or the aircraft. Engine power was used to climb back onto the taxiway and we returned to the ramp for a full inspection. No noticeable defect was noticed and mechanics were scheduled for a more in depth inspection the following day.As a Flight Instructor I was surprised that my student would want to continue the flight after something like this happening. He; the owner; was angry that I did not want to continue the flight. This served as a reminder that no matter what the circumstances as a Flight Instructor with a Student Pilot on board I am always pilot in command.