The flight instructor in the amphibious float-equipped, weight-shift aircraft reported that the accident flight was the third flight with the student pilot, and the student pilot's first flight in the front seat. He further reported that during the takeoff roll they "began to [lose] the center line to the left and then to the right." He reported that in this particular aircraft, to turn to the right you push the left pedal and to turn to the left you push the right pedal. He instructed the student pilot to release the throttle. He then attempted to "take the controls back and keep the [aircraft] on the runway", but was unsuccessful. The aircraft veered off the runway to the right, the right float impacted grass, and the aircraft spun 180 degrees. The student pilot reported that he told the flight instructor that he would "follow along with him on the controls during the takeoff to feel how he was moving them". He further reported that when the aircraft veered off the runway to the right, he "took [his] hands off the controls" to allow the flight instructor to correct for the veer. The aircraft sustained substantial damage to the right lift strut. The flight instructor reported no preaccident mechanical malfunctions or failures with the airplane that would have precluded normal operation.