On May 13, 2000, at 1300 hours mountain standard time, a Piper PA-32R, N4148R, lost engine power and made a forced landing on a highway near Casa Grande, Arizona. The aircraft sustained substantial damage; however, the certified flight instructor and student were not injured. The aircraft was being operated as an instructional flight by Sabena Airline Training Center, Inc., under 14 CFR Part 91 when the accident occurred. The flight originated from Scottsdale airport in Scottsdale, Arizona, about 1145. Visual meteorological conditions prevailed at the time and no flight plan was filed. In a telephone interview, the flight instructor said that the student, who was under the hood, was preparing to execute an approach to Casa Grande Municipal Airport. Part of the landing checklist included switching the fuel selector to the fullest tank; however, the student inadvertently switched the selector to the "off" position. When the engine quit, the student verbalized the emergency checklist items sequentially to the instructor who performed the required actions. The student omitted the first item (switch to fullest tank) because of having already switched. The instructor was unable to restart the engine within the time and altitude remaining and executed a forced landing on Highway 84 near the intersection with Bianca Road. During the landing, the right flap struck a cement bridge stanchion and the left wing struck a tree. Once on the ground, the instructor identified the fuel selector as having been in the "off" position. A recommendation for accident prevention was prepared by the Federal Aviation Administration (FAA) Flight Standards Division Manager in Arizona. According to the FAA report, the fuel selector stop is mounted on a plastic center fuel panel on the floor between the pilot and co-pilot seats. Upon removal of the panel, it was found that the stop for the steel spring arm was bent, allowing the selector to travel to the "off" position. No action to press it down as a separate and distinct action resulted. The bend was not evident while the panel was mounted in place. The design of the fuel selector, part number 69654-22, for the Piper Saratoga and all like components were to be evaluated. The current design provided a positive stop, but was not designed to prevent improper use and eventual wear.