On June 5, 2000, about 0800 hours mountain standard time, a Beech 95, N133PW, sustained substantial damage when the landing gear retracted during takeoff from Sun Valley, Arizona. Sheble Aviation, Bullhead City, Arizona, operated the airplane under the provisions of 14 CFR Part 91. The certified flight instructor and the private pilot student were not injured. Visual meteorological conditions prevailed and no flight plan had been filed for the instructional flight. According to a pilot-rated witness, the airplane was on the takeoff ground roll when all three landing gear retracted prior to rotation, and the airplane settled back to the runway. The left wingtip struck the runway and the airplane cartwheeled, running into a rising dirt embankment, and coming to rest on the side of the runway. The witness went to the assistance of the airplane occupants and spoke to the flight instructor. According to the witness, the instructor said that the student might have placed the landing gear selector switch in the up position instead of the flaps after the previous landing. In his written statement, the flight instructor reported that the nose gear collapsed during the takeoff ground roll. He had no further explanation of the event. A review of the Beech Model 95 Travel Air Owner's Manual reveals an excerpt from the normal takeoff procedure and reads: "Retract the landing gear as soon as you are firmly airborne with no danger of settling back to the runway."