This paper examines how Chinese (n = 11) and Spanish (n = 11) preservice teachers reflect on their learning-to-teach experiences during the teaching practicum period through the lenses of transformative learning theory and third space conceptualisation. Specifically, the authors adopted the five-stage transformative learning model and collected reflective journals from the participants. Framed by this model, the authors traced the Chinese and Spanish preservice teachers' transformative professional learning experiences evidenced by (1) disorienting dilemma, (2) reflection and exploration of assumptions, (3) gaining confidence in a new role, (4) behaviour changes, and (5) integration of new perspectives. Implications for fostering a third space, namely hybridity and boundary-crossing between university and schools, during teaching practicum are discussed in this paper.