On February 3, 2016, about 1130 Pacific standard time, a Cessna 172S, N499DR, impacted a parked, occupied Cessna 172S, N1955L at the Gillespie Field Airport (SEE), San Diego/El Cajon, California. Both airplanes were occupied with one certified flight instructor (CFI) and one student pilot; no one was injured. N499DR sustained minor damage, and N1955L sustained substantial damage to the fuselage structure and rudder. Both airplanes were registered to Sorbi Aviation Inc., and were operated by the California Flight Academy as 14 Code of Federal Regulations Part 91 instructional flights. Visual meteorological conditions prevailed at the time of the accident and neither airplane had filed a flight plan. Both airplanes were on the California Flight Academy parking ramp preparing for their local flights. The CFI from N499DR reported that this was the student pilot's first flight lesson. After completing a thorough preflight they hand towed the airplane out from its north facing parking spot and turned it towards the east. They started the engine and it idled between 800-1000 RPM. While listening to the airport's automatic terminal information service (ATIS) the airplane started to move with a right turning tendency. The CFI stated he did not notice it at first, but when he did, he stepped on the brakes. The airplane increased its right turn and struck a parked, occupied, airplane (N1955L). In a later conversation, the CFI reported that when he attempted to stop the airplane he noticed that the right rudder pedal was slightly more forward than the left, but not by much. In a written statement, the student pilot from N499DR reported that when the CFI was listening to the radio, the airplane started moving and turning into another airplane. He stated "Hey you! Airplane is moving!" and he touched the CFI. The CFI looked at him, then back at the radio, and he "did not do anything;" he appeared to be distracted. The airplane continued its turn and impacted N1955L. The CFI of N1955L reported that the student pilot and he were preparing for their flight with the engine off, when they suddenly felt a jolt and heard the sound of metal contacting metal. They turned around and observed that N499DR had struck the aft fuselage of their airplane. During a postaccident examination of N499DR's brake system by a Federal Aviation Administration airworthiness inspector, there were no visual defects or leaks. He manipulated the brakes both dependently and independently with no anomalies noted.