This thesis is an attempt to survey the effect of method of discovery instruction in assuming the following hypotheses. And this research is adopted the first grade in a middle school as the object of study. Hypothesis I: Discovery instruction may be more advanced the level of attainment of learning and the scientific attitude than traditional-expository-instruction. Hypothesis II: According to the degree of the intellectual development, discovery instruction may have a different effect on the level of attainment of learning and the scientific attitude. To verify above two hypotheses, the two classes of the first grade from D middle girl school in Seoul is taken samples and, adopting the biological lesson as the learning subject matter, one Mass applying traditional-expository-instruction as the controlled group and the other class applying discovery instruction as the experimental group is each selected. And before this, to verify the homogeneity of those groups, I.Q., the results of examination in science, and the scientific attitude is investigated: Upon this investigation, the two groups is, proved to have the homogeneity. After giving lessons to the two groups through the nine tunes, the level of attainment of learning is estimated in classify ing the knowledge the apprehention, and the application, while the scientific attitude is investigated in classifying the recognition, the interest, and the attitude, on the science. In this research, T-verification is used for the hypothesis-verification as the statistical method and the intention level standardizes P=0.05. The- results are: 1) Comparing between discovery instruction and traditional-expository-instruction, the former is more effective in the sphere of the intellectual(the level of attainment of learning) and of the sentimental(the scientific attitude). 2) Discovery instruction differs with the effect of it in proportion to the gradation of the intellectual development. it is more effective in the sphere of the sentimental in the superior group, while it is far effective in the sphere of the intellectual in the inferior group. On the basis of above results, discovery instruction has more facilitating effect on attaining the object of scientific studying in a scientific lesson than traditional-expository-instruction. Moreover, the former can be given rise to motive of the next lessons and realized the highly motivated lessons to the inferior group by the successful attainment of studying. That has prevailed a profound significance of the method of discovery instruction.