Background The curriculum for the courses given at the music specialization of the upper secondary school’s aesthetic program in Sweden includes the concept of artistic expression (AE). Being a criterion for assessment, no definition is provided by the National Agency of Education and there exists no consensus of how to interpret artistic expression among music teachers and music teacher students. Methods In order to explore how teachers understand, teach, and assess the concept and phenomenon of artistic expression, twelve qualitative interviews with music teachers were conducted and analyzed through an open coding process. Results The findings show that the concept of artistic expression is multifaceted and evasive. The results focus on two analytic threads: (i) situatedness and (ii) entanglement. (i) AE is situated due to context-specific parameters which underpins the meaning of the concept in this particular educational setting. (ii) Furthermore, the phenomenon of artistic expression is entangled (a) with the ongoing relationship between teacher and student, and (b) in a temporally unfolding and interactive musical event. The phenomenon of artistic expression as entangled is discussed, primarily through Hartmut Rosa’s concept of resonance, which brings into focus the intersubjective character of aesthetic experience. Doing so questions understandings of – and assessment procedures surrounding – artistic expression that relies on skill-based interpretations or reductions of entanglement. One example of such reduction is assessment of recordings of student performances which limits (a) the relational perspective (if assessed by a third person) or (b) the entanglement with the musical event. The perspective of resonance brings forth the teacher’s role during a student performance as characterized by self-efficacy and active listening, thus co-constitutive of artistic expression. Conclusions The article concludes with reflections on how the findings may contribute to the continuous discussion on how scientific grounding and proven experience may inform both the music education at upper secondary school and music teacher education. The concept of resonance provides a possibility to reframe conceptions of artistic competence in art education as being grounded in intersubjective and relational terms, rather than being reified as a set of measurable skills, an understanding which in turn risks replacing learning with criteria compliance.