Ⅰ. problem The Present investigation attempts to study the effects of advance organizers on learning by varying individual difference of previous learning with relation to the materials to be learned. Advance organizer is used to designate more complex and deliberately prepared sets of ideas which are presented to the learner in advance of the body of materials to be learned. Ⅱ. Hypothesis The following hypothesis was derived to be tested in the investigation. The difference between A and B is larger than that of C and D. * Symbols of A, B, C and D are used to indicate the gain scores between the pretest and post-tests of the following groups. A is of group having lower availability of relevant ideas previously learned and equipped with advance organizers. B is of group having lower availability of relevant ideas previously learned and not equipped with advance organizers. C is of group having higher availability of relevant ideas previously learned and equipped with advance organizers. D is of group having higher availability of relevant ideas previously learned and not equipped with advance organizers. Ⅲ. Methods 1. A. Independent variable in the study is as follows: (a) Relevant ideas previously learned make possible for the students to learn learning materials (Mendel's law). The ideas relevant to learning Mendel's law include dominance, inferiority, hybrid, other-pollination, gene, fertilization, a full blood, characterizer, pollination and self-pollination. (b) Introductory material (1) The experimental group studied introductory material (advance organizers), pointing out the relation between deminance and inferiority. (2) The control group studied nonideational introductory passages concerning Mendel's life. (c) Learning material was consisted of Mendel's law. B. Dependent variable is the scores of achivement test consisted of ideas instructed in the learning material. 2. Subjects and procedure The subjects of this study consisted of four classes which were selected from the eighth grade in a middle school in Seoul area. The total number of the subjects was 249 school boys. Of the four classes, two classes were assigned to the experimental group of this study: and the other two classes to the control group. Although each student had been randomly assigned to aclass at the beginning of the semester, an analysis was made to check the homogenity of the experimental and control groups. It was shown that the two groups were not significantly different in IQ and pretest of availability. On the first day of experimentation, all subjects took a learning session which instructs the ideas relevant to learning Mendel's law for 20 minutes. Two days after the first experimental session, all subject took a test of the ideas relevant to learning Mendel's law. They studied either the advance organizer or the historical introductory passage about Mendel's life for 10 minutes, and studied Mendel's law for 30 minutes. The test on the Mendel's law passage came 4 hours later. Ⅳ. Results In ordervto test the hypothesis, analysis of variance was applied. 1. The gain score of experimental group was found to be larger than that of control group. This finding was significant at the level of 1% (p＜.01). 2. In the experimental group, the gain score of group having lower availability of relevant ideas previously learned was found to be larger than that of group having higher availability of relevant ideas previously learned This finding wasaccepted at the level of 5% (p＜.05). 3. In the control group, the gain score of group having higher availability of relevant ideas previously learned was found to be about the same that of group having lower availability of relevant ideas previously learned. This finding was accepted at the level of 10%(p＞.05). According to these results, it can be said that the hypothesis in this study was confirmed. The results indicate that advance organizers facilitate learning, and that the use of advance organizers is necessary for the group having lower availability of relevant ideas in learning.