As the student jumper was getting out of the aircraft and onto the step in preparation for a parachute jump the pack tray prematurely opened and the canopy blossomed under the tail pulling the jumper into the horizontal stabilizer causing a cut on his left shin. About 15 inches of the right horizontal stabilizer and elevator were sheared by the jumper. The remainder was crumpled and deformed from mid-span outward. A witness stated that the only way this could happen was if the pilot had the yoke back and the tail low. In other premature openings the witness had been involved with, the parachute opened under the tail and the jumper also went under the tail clearing the aircraft structure in all cases.