In Japanese tutoring school industry, the share of private-tutorial schools, which can meet a wide range of student needs, is increasing compared to traditional group-type tutoring schools. However, the future trend of declining birthrates, the private-tutoring schools need to take measures to ensure future business growth. For business growth, that is, continuous sales and profit expansion, one of the effective strategies is utilizing low-cost part-time teachers who can be hired easily due to the large number of candidates. However, the variabilities in experience and skills of part-time teachers generally cause low quality and low efficiency in class operations. Therefore, improvement in quality and efficiency in class operations by part-time teachers tend to become challenge for the strategy.In this paper, we investigated the class operations in a private-tutoring school and extracted problems related to quality and efficiency. As a result, it was found that many of the extracted problems were caused by human error related to experience and skills of part-time teachers. To reduce the human error, we have developed a standard process for class operations of teachers.The developed standard process was evaluated for one month by six part-time teachers at the privatetutoring school. The class operations were compared these with before the introduction of the standard process. As a result, the ratio of human errors in problems occurred in class operations improved by17 points. The results indicate that an introduction of the developed standard process leads to reduction of human error in class operations in private-tutorial schools.