A Piagetian type task, The Island Puzzle, was administered to children grades 5 to 12, to science teachers attending a National Science Teachers Association Convention, and to college physics teachers attending a regional meeting of the American Association of Physics Teachers. The procedures differed from those of Piaget in that the puzzle was administered to a group of subjects and the individual responses were written. Subjects participating in the study were shown a map of four islands and a puzzle involving flights from one island to another was presented along with clues. Three questions were asked about whether flights could be made between certain islands. Answers to the questions were grouped into six different categories. A total of 449 subjects were involved in the study. Results of the study indicate that intellectual development in abstract reasoning progresses gradually from grade 5 to grades 10 to 12, where little further progress is made and abstract reasoning reaches a plateau. The sequence of six categories established in this study appear to be very close to the sequence Piaget and his collaborators have found applicable to the tasks investigated by them. (BR)