GA Flight Instructor with student reported during takeoff roll at a non-towered airport; a non-communicating aircraft took off from opposite-end runway causing the instructor to reject takeoff and maneuver to side of the runway.

Narrative

I was departing from HEG at XA:50 in the morning. The winds were variable and the runway traffic was using was inconsistent. Before we taxied; my student did a comp check and we were received loud and clear. We decided to use runway seven at her long due to winds favoring that runway and several landing aircraft using that runway. After our run up at a plane took runway 25 so we held short to wait till after they left to depart. After they departed; another plane used 7 to land and we were about to take the runway after them when a third plane took 25. After that plane was clear we announced we were taking to seven for takeoff. We added full power and at around 20 kts we saw a plane at the other end of the runway using 25. They were already off the ground and cleared us by several hundred feet as soon as we saw them; we immediately reduced power applied breaks; and maneuver to the right side of the runway. There was no call or communications from the other aircraft. Between the lack of communications from the other plane and the hump in the middle of the runway there was no way to have known they were departing 25.