  This article reports on an investigation of student understanding of the
concept of time in special relativity. A series of research tasks are discussed
that illustrate, step-by-step, how student reasoning of fundamental concepts of
relativity was probed. The results indicate that after standard instruction
students at all academic levels have serious difficulties with the relativity
of simultaneity and with the role of observers in inertial reference frames.
Evidence is presented that suggests many students construct a conceptual
framework in which the ideas of absolute simultaneity and the relativity of
simultaneity harmoniously co-exist.
