In recent years, music therapy has become an increasingly popular method used as an intervention in the rehabilitation of children with Autism Spectrum Disorder (ASD), conducted by professionally trained music therapists. Music is a more efficient medium for communication, self-expression, and interaction for children than other forms, since it facilitates comprehension and assimilation. However, before a claim on the effectiveness of these interventions can be made, additional high-quality studies consistently proving their efficacy for individuals with ASD are needed. This study observed the impact of music therapy on joint attention in three preschool-aged children with ASD. All three children participated in ten individual music therapy sessions held 1-2 times per week. Active music therapy was applied through techniques such as improvisation, performance, imitation, mirroring, etc., with careful adaptation of instrument choice and activities to each child. First, the results of the qualitative assessment conducted by a music therapy student were presented, with numerical values assigned and compared with the quantitative assessment by a rehabilitation specialist. Given the positive changes in both assessments, it can be said that music therapy can improve joint attention in children with ASD and that both quantitative and qualitative assessments are applicable for demonstrating this. In this study, qualitative descriptions detailed all moments of attention, what triggered it, and what interrupted it, while the quantitative assessment provided a visual and numerical representation of the progress toward set goals through therapy, i.e., the evaluation of the therapy. The qualitative music therapy assessment can additionally provide insights into certain elements not registered through standardized scales, such as changes in tempo, dynamics, instrument choice, manner of vocalization, movement, etc.