A witness saw the airplane as it was maneuvering in the vicinity of the accident site. The airplane was then observed to enter a spin and disappear behind trees, where it impacted in a plowed field. Examination of the airplane failed to disclose a mechanical problem. There was evidence that the airplane impacted the ground in a stalled attitude. Both wing assemblies sustained aft crushing damage to the leading edges. The student pilot's medical certificate was dated 8/11/93. No pilot flight logs were recovered for examination.