During a practice touch and go landing on a check flight for a pilot, new to the airplane, the pilot receiving the check lost directional control of the tail wheel equipped airplane on the landing roll and drifted towards the right. The check pilot did not act in a timely manner to prevent the airplane from departing the runway's edge. The airplane subsequently struck a drainage ditch and sustained substantial damage to the fuselage. The pilots reported no preimpact mechanical failures or malfunctions with the airplane that would have precluded normal operation.