Flight Crew Commercial; Flight Crew Multiengine; Flight Crew Instrument; Flight Crew Flight Instructor
Flight Crew Last 90 Days 110; Flight Crew Total 1325; Flight Crew Type 320
Communication Breakdown; Human-Machine Interface; Situational Awareness
Conflict Ground Conflict; Critical; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy; Ground Incursion Taxiway
Flight Crew Took Evasive Action
Human Factors; Procedure
I was training a primary student.  We received clearance from the ground controller to taxi to the runway and contact tower.  As we taxied onto the taxiway; Aircraft Y with an elderly gentleman operating single-pilot at the controls was parked facing the taxiway at a perpendicular angle in the run-up area.As we neared this airplane while taxiing down the taxiway toward [Runway] XXR abeam intersection 1; he started moving forward while looking to the left.  We got within 20-feet of each other and he never noticed because he failed to clear to his right prior to taxiing onto the taxiway.  This other pilot failed to request a taxi on ground from the run-up area as is our local procedure.We slammed on our brakes; coming to an abrupt stop and avoided the collision.
Instructor Pilot reported braking hard to avoid a collision with another aircraft during taxi.