Group music making has the potential to develop socio-emotional competences. This study describes how responsibility and respect--both of which are socio-emotional competences--were developed through a socio-musical program, called "Musiquem," in a Spanish primary school. The research consisted of a case study with students from Grades 3 to 5 (aged from 9 to 11) carried out over 1 school year (2018-2019). The program was developed as a specific music project to create a string orchestra and was implemented by two specialists in the violin and cello working in collaboration with the teachers in the primary school. The study describes the characteristics of the activities carried out to develop respect and responsibility and the results suggest they have a positive impact on students' development of these socio-emotional competences.