The positive role of metacognition in music learning and practice is well assessed, but the role of musicians' metacognitive skills in such a context is not yet clear. Teachers often state that they apply a metacognitive approach during their lessons, but students fail to acknowledge it and report that they become metacognitive learners thanks to their own practice. In this multiple case observational study the spontaneous metacognitive behaviour of a teacher during four piano lessons with expert and novice students was analysed. Data supported the notion that teachers use metacognitive strategies during their teaching practice, but students are not aware of this because a metacognitive focus on strategies, as well as a strong emphasis on monitoring, appears to be lacking. Teachers are also able to differentiate their teaching behaviour between expert and novice students. Students' age, however, affects teachers' behaviour more deeply than expertise. Implications for music education are discussed, highlighting the main issues that can be derived from the results and how they can be effectively used to enhance professional development and improve practice in music education.