This paper analyses the factors affecting the acquisition of metallophone in primary school music lessons. The aim of the study is to determine the factors that affect the primary school student's performance while playing the metallophone in the classroom and to identify the factors that might be subject to change in case of repeating the performance. To achieve this aim, previous studies which focused on the impact of playing musical instruments on the students' musical, general and intellectual development have been analysed, and an empirical study on the factor affecting the acquisition of playing the metallophone was carried out. The study took place in two general education schools located in different Latvian cities during the period from March 2018 to May 2018, with a sample of 105 students (N=105) in the 3rd-grade. In order to identify the factors that might affect the primary school student while playing the metallophone, each student had to perform two exercises on the metallophone. After each exercise, the student was asked to complete a self-assessment questionnaire. The study identified four key factors determining the acquisition of metallophone, which are reflected in this paper as study dimensions: initiative, self-confidence, self-control, and achievement orientation. The study found that none of the factors that affect the acquisition of metallophone was at a low level. The students' achievement orientation was at a high level, which means that the students were interested in using metallophone to play both exercises. The students have assessed the self-control dimension at a middle level, which means that the self-control skills of the 3rd-grade students still need to be improved by encouraging them to continue practising on the musical instrument. Repeating the same exercise on the metallophone has shown that the students examine the correctness of their performance, are more restrained and more confident that they will achieve the goal. The study result provides an opportunity to better understand the impact of the initiative, self-confidence, self-control, and achievement orientation on the acquisition of playing the metallophone in primary school.