The pilot receiving instruction in the multiengine airplane reported that, during the runup, he and the flight instructor briefed for a simulated engine failure during takeoff. He added that, during the takeoff, the instructor reduced the left engine throttle, and the airplane veered left. He "lost the control," and the instructor took the flight controls. The airplane lifted off into ground effect, the left wing struck the ground, and the airplane then exited the runway and came to rest in grass. The instructor, who was seated in the left seat, reported that, after he reduced power on the left engine during takeoff, the pilot became confused by the sudden left yaw and did not react. He repeatedly told the pilot to abort the takeoff. Brakes were only installed on the pilot's (left) side, so the instructor was unable to apply brakes. The pilot panicked, moved the left throttle to full, remained locked on the controls, and applied back pressure on the yoke. The instructor continued to attempt to take the flight controls from the pilot, but the airplane entered ground effect. The instructor eventually took the flight controls, and as the airplane settled to the ground, he reduced both throttles to idle. The airplane touched down in a "left yawing, slight left bank attitude," and the landing gear collapsed. The airplane skidded on the runway to the left, rotated counterclockwise, exited the runway, and then came to rest in grass. The airplane sustained substantial damage to the left wing. The pilot and instructor reported that there were no preaccident mechanical failures or malfunctions with the airplane that would have precluded normal operation.