On April 1, 1998, approximately 1110 Pacific standard time, the left wing of a Beech 35-C33, N1310A, impacted the runway immediately after a premature liftoff at Portland-Hillsboro Airport, Hillsboro, Oregon. The certified flight instructor and his student, who holds a private pilot certificate, were not injured, but the aircraft, which was owned and operated by Tektronix Flying Club, sustained substantial damage. The 14 CFR Part 91 local instructional flight was being operated in visual meteorological conditions. No flight plan had been filed, and there was no report of an ELT transmission. According to the FAA inspector who talked to the instructor, while practicing soft-field takeoffs, the student pulled the aircraft into the air prior to attaining enough speed to remain airborne. The aircraft almost immediately banked sharply to the left, and dropped back onto the runway hard enough to be "jolted" back into the air. The takeoff was then continued, followed by an immediate return to inspect for damage. According to the instructor pilot, when the aircraft, which was configured with a single throw-over control yoke, began lifting off, he commanded the student to "drop the/your nose." The student did not drop the nose enough to avoid the premature lift-off, and the instructor did not attempt to apply forward pressure on the central control pedestal to keep the aircraft from lifting off too early.