On February 11, 2006, about 1510 Pacific standard time, a taxiing Cessna 172N, N739GY, collided on the ground with a standing Cessna 172P, N54661, at Sacramento Executive Airport, Sacramento, California. Executive Flyers, Inc., was operating both of the airplanes under the provisions of 14 CFR Part 91. The private pilot and one passenger in the taxiing Cessna 172N were not injured; the airplane sustained minor damage. The certified flight instructor (CFI), the student pilot, and one passenger in the standing Cessna 172P were not injured; the airplane sustained substantial damage. The Cessna 172N was preparing to depart on a local personal flight, and the standing Cessna 172P was departing on a local instructional flight. Visual meteorological conditions prevailed, and no flight plan had been filed for either airplane. The CFI in the 172P stated that he and his student were in the run up area. Their airplane was stationary, and he saw the pilot of the 172N stop behind him. After completing their takeoff checks, they switched from ground control to tower frequency. He heard the 172N pilot ask and receive clearance for takeoff. He saw the 172N move forward, and felt that it was getting too close to his airplane. He was about to move forward when the left wing of the 172N hit his airplane's rudder. The pilot of the Cessna 172N stated that he positioned himself behind the 172P in the run up area. He completed his checklists, and requested takeoff clearance. He received permission to position and hold, and added power to taxi around the 172P. He said that he failed to realize the close proximity of his airplane's left wing to the 172P's rudder. His airplane's wing tip collided with the other airplane's rudder and vertical stabilizer. Both pilots immediately stopped and shut down their engines.