Form and Content in the Development of Deductive Reasoning

8th graders gave complete falsification solutions 29% of the time, 10th graders, 42%, and 12th graders, 46%. When only the three familiar problems are considered, 8th graders gave complete falsification solutions 48% of the time, 10th graders, 62%, and 12th graders, 68%. A test for the difference between two proportions revealed that only the 12th grade selected this solution more frequently than the 8th grade, z = 2.33, p < .05. The percentages for the familiar problems are presented graphically in Figure 1. Confidence that an individual possesses a formal logical competence is increased to the extent that the individual is consistent in presenting logical solutions. As a consequence, a final developmental comparison was made of subjects who consistently gave complete falsification solutions across familiar problems. Because the subjects performed significantly more poorly on one of the problems (the school problem, discussed later) it was not included, and the consistency score for each subject was the complete falsification solution on each of the two remaining problems. Expressed as percentages of total number of subjects at each grade level these scores are 8th grade, 45%; 10th grade, 68%; and 12th grade, 86%. A test for the difference between two proportions indicated that the 12th graders were more consis-