The student had completed about seven hours training and was undergoing her second session of circuit training. The instructor stated that the student had previously had difficulty with the directional control of the aircraft. On this takeoff he allowed the student to manipulate only the rudder, so that she could concentrate on the directional control aspect, while he manipulated all the other controls. As the power was increased the aircraft gradually swung to the left. Approaching the left side of the strip the swing increased and the instructor applied right rudder at the same time as the student. The aircraft swung to the right and as it crossed the right side of the strip the left wheel dug into the ground and the aircraft tipped onto the left wing.