The purpose of this study is to analyze the process of the acquisition of vocal skills of a choir of approximately 90 boys (aged 8-12) in “Gyosei Elementary School” and to identify the necessary teaching conditions. The data collected through observations of the choir and interviews of the teacher were analyzed based on the grounded theory approach, focusing on the situation in which pupils were trying to overcome their vocal difficulties through the interaction with their teacher. Through this data analysis, a main category “teachers' comments and advice to pupils” along with seven sub-categories were identified. The following three points were found to be salient factors in the acquisition of vocal skills for elementary school pupils : (1) it is important for pupils to keep practicing simply and concretely, (2) the teacher should adopt various ways of teaching to realize problems pupils may have, to improve contents of practices, and to check frequently if the children have mastered the skill, (3) teachers sometimes have to disregard some vocal issues to keep pupils' motivation and protect their immature throats from over practice.