As our life becomes more sophisticated, our ability to create concepts is indispensable. Based on our concept formation model, which focuses on ambiguous items that cause a change of one's decisions, we developed a web-based creativity support system. This is intended to guide users in the categorization of words in analogical reasoning by forming batches of words to discover new concepts. 20 junior high school students participated in an experiment, where concept formation is expected to be induced by an ambiguous interpretation of presented information under constraints. The result provided some evidence that an existence of ambiguous items corresponds to a diversification of a thought process either as insight or trial & error in categorizing words. The result also showed that the reconstruction of groups for including ambiguous items into some groups accelerates the creation of new concepts for better interpretation.