This presentation examines how teachers’ professional development can support equity, well-being, and improvisation in compulsory school music education, drawing on key results from a researcher-facilitated development process with two arts teachers in Finnish upper secondary education as part of a Kone Foundation-funded three-year project (2023-2026). The project emerged from concerns over students’ increased malaise, weakened social community, and difficulties in connecting school with future life (THL, 2025), alongside evidence that music’s well-being benefits tend to accrue to students engaged in extra-curricular music-making (Fancourt & Finn, 2019; Juntunen, 2019). The development process unfolded in a context where students’ experiences of compulsory music education were highly polarised, with communality central to participation and learning often perceived as secondary (cf. Siljamäki et al., 2026a; Siljamäki et al., 2026b). The theoretical framework approaches education as relational, understanding professional development as emerging through ethical responsibility, dialogic researcher-teacher collaboration, and teachers’ professional judgement in response to student vulnerability; teachers’ beliefs further shape what kinds of pedagogical change become possible in practice (Akkerman & Bakker, 2011; Appova & Arbaugh, 2018; Biesta, 2010; Biesta, Priestley & Robinson, 2015; Boylan et al., 2018; Khong et al., 2023; Noddings, 2013). Within this framing, improvisation is conceptualised as an inseparable part of music-making and a universal, accessible creative capacity (MacDonald, 2022), introduced through the researcher’s expertise in applied, artistic, and pedagogical improvisation (Siljamäki, 2023) and used as a shared pedagogical context for exploring wellbeing, participation, and safety in classroom settings. In this qualitative interpretive study (Denzin & Lincoln, 2018), a music teacher and a theatre teacher engaged in workshops, mentoring, and classroom experimentation with the PI-researcher during 2023-2024. Data included teacher interviews, reflective workshops, classroom observations, and documentation of pedagogical trials, analysed through close reading and thematic comparison focusing on changes in pedagogical decision-making (Braun & Clarke, 2006, 2019). Findings show that pedagogical reorientation emerged through collegial trust, dialogic reflection, and ethical urgency prompted by student vulnerability. Teachers experimented with and integrated improvisation within existing practices, with beliefs about art, learning, and responsibility shaping what kinds of change were possible. Improvisation functioned as a pedagogical context for recalibrating participation, safety, and responsibility in both the teacher-researcher dialogic space and everyday classroom practice. Also, the findings reflect the limits of pedagogical change in a context marked by student distress and polarised experiences, highlighting how efforts toward equity and wellbeing are constrained by broader school conditions and increasingly fall on teachers as emotionally demanding and largely solitary work.