Australian initial teacher education accreditation requirements have, since 2016, mandated a capstone teaching performance assessment (TPA) to assess pre-service teachers (PSTs) against the Australian Professional Standards for Teachers. This research examines how a standardised TPA known as the Assessment for Graduate Teaching (AfGT) can impact on PSTs' readiness to teach. The AfGT comprises PSTs' analysis of their teaching practice using video of teaching episodes, observation feedback, and students' work samples augmented by an online situational judgement task. The researchers used thematic data analysis of surveys to investigate how the AfGT impacted on PSTs' perspectives of what matters in teaching. The research established that the process of completing the TPA can activate and reinforce reflection and professional reasoning, and expand PSTs' knowledge of how their teaching improved student learning. The results provide insights into how a complex and high-stakes TPA can foster professional growth while signalling key enabling conditions.