Music therapy has been shown to be efficacious in experimental studies. However, there is little empirical research knowledge about what elements of music therapy influence its effectiveness in clinical practice. Children and adolescents with psychopathology (N=75) were assessed before and after participating in individual music therapy with 1 out of 15 music therapists in the Vienna region. Relationships between outcomes (as evaluated by parents) and therapy contents (as reported by therapists) were examined using general linear modelling. Results indicated that clients' symptoms and burdens on their social environment showed greater improvement when music therapy was limited to discipline-specific music therapy techniques and did not include other media such as play therapy elements. The findings indicate the importance of being aware of a therapy method's specific strengths and limitations. More research on the indicated specific ingredients of music therapy intervention is needed.