The quality of interactions among small group members constitutes a significant factor that brings about positive effects in school learning. And aspects affe cting the quality of the interactions are still more numerous. In this study, we chose one of the important aspects, namely: “the effects of teaching activities”, and examined the reasons why the activities would produce good results in small groups. Two types of instructions were given...A: “You must teach another person after learning yourself”, B: “Your attainment will be evaluated after you have learned”. Two types of activities were directed after a study lasting 25 minutes. a: To teach another person, b: To review the learning tasks. E1 was the condition of and E2: A+b, and C B+b. Ss were 11 2 year-old children, and the tasks used were arithmetic. Results were as follows.(1-) 1 The learning set to teach another person “after one has learned” had positive effects on academic achievement.(2) The activities to teach another person seemed to have a possibility to raise some positive effects.