Two experiments were designed to assess the effects of focus instances on learning of scientific concept. In Experiment I, two kinds of reading materials were constructed describing common features of metal. The text given to Cu group explained those features by referring to copper. For Ca group, calcium was used. As a result, Ca group showed better performance in the test for classifying instances into metal and nonmetal while the Cu group showed better performance in the recall-application test for common features. In Experiment II, two kinds of reading materials were constructed describing a universal property of livestock. The text given to Bl group explained that property by referring to swine. For Kl group silkworm was used. As a result, Kl group showed higher score in the test for classifying animals into livestock and non-livestock while the B1 group showed higher score in the recall-application test for a universal property. The obtained results were discussed in terms of the difference of information that Ss received from focus instances. Finally the author proposed a new theory called “heteroformulation theory”.