To assess the effects of focus instances in concept learning, three kinds of reading materials were constructed describing common features of metal. The reading materials given to Cu group and Fe group explained those features by referring to copper and iron respectively which Ss regarded as metals. For Ca group, calcium regarded as non-metal by Ss was employed. The main results were as follows. In the test for classifying various instances into metal and non-metal, Ca group showed better performance than other groups. In a recall test for common features, the marks of Cu group and Fe group were higher than those of the third one. The obtained results were discussed in terms of the differences of information that Ss received from focus instances.