An experiment in teaching logic to fifth graders using a children's story is reported. Part one of the report develops the experiment's rationale. A lack of reasoning ability among children is perceived and several causes are suggested -- among them a reliance on reading, math, and science as vehicles for reasoning, emphasis on problem solving rather than the preliminaries of questioning, and complacency regarding the development of reasoning because of the "inevitability" of development implied by Piagetian research. To allow children to perceive themselves capable of reasoning, instruction in reasoning for fifth graders is proposed. Instruction combining a discovery model and a context of "important" ideas is suggested. Part two of the report describes the experiment. A pilot group of 10-year-olds, taught twice a week for nine weeks using the story, "Harry Stottlemeier's Discovery," (SO 008 127), is tested against a control group. Instruction consists of reading, discussion, some role playing, and use of a video tape machine. Posttesting shows an advance by the pilot group over the control group in logical thinking and in mental maturity. A second study testing the same two groups indicates a significantly positive effect on the reading scores of the pilot group over the control group 2 1/2 years later, suggesting the long lasting effect of the teaching of logic and the need to replicate the experiment. (JH)