The purpose of the study was to make clear the difference of verbal behaviors of both teachers and pupils resulted from the degree of skillfulness of the teachers. Four teachers gave instructions in arithmetic (teaching about "calculation and formula") at four homogeneous classes of the 4th grade respectivery under the same teaching materials and under the same teaching program. These classes were tentatively named class No.1, No.2, No.3, and No.4. The teachers of class No.1 and No.3 were class teachers and the teachers of class No.2 and No.4 were university student who had finished the teaching trainings for three weeks. The results were followings: 1. In the first one minute of the instructions, the teachers of class No.1 and No.3 introduced the present subject with a short review of the previous lesson, though the teachers of class No.2 and No.4 introduced abruptly the present subject. 2. From the analysis of durations of teacher's speakings and pupils' speakings through the instructions, it was found that in the class No.1 and No.3 the total durations of teacher's speakings were longer than those of pupils' speakings, and that in the class No.1 and No.3 durations of teacher's speakings and pupils' speakings were greatly changing through the instructions, but in the class No.2 and No.4 those were comparatively even through the instructions. 3. From the analysis of categories of the teacher's speakings, it was found that in the teachers of class No.1 and No.3, there were many speakings belonging to "management", "confirmation", and "nomination", and that in the teachers of class No.2 and No.4, there were many speakings belonging to "whisper", "not understandable", "direction", and "confirmative question". 4. From the analysis of categories of pupils' speakings, it was found that "answer" was conspicuous in class No.1 and No.3, but "receptiveness" was often observed in class No.2 and No.4.