This study was concerned with distinguishing between two kinds of immature reasoning, both of which lead children to draw the same conclusions from arguments and which, therefore, cannot be distinguished by the usual tests. A total of 20 second-graders and 16 sixth-graders were tested on a logic game in which winning depended on drawing correct conclusions from logical arguments and on using only the minimum amount of evidence necessary to reach such conclusions. Results indicated that younger subjects drew significantly more conclusions from circumstantial evidence and more often treated logically critical clues as indeterminate. Subjects at both grade levels showed a strong tendency to commit the fallacy of conversion, but older subjects showed improvement in response to feedback. These results support Piagetian stage theory with respect to verbal reasoning. Younger subjects were seen as reasoning in an intuitive, factual manner, while older ones were seen as reasoning from a logical system, albeit a simplified system that erroneously treats conditional statements as reversible. (Author/SB)