Although the importance of practicum for preservice teachers goes almost unchallenged, specific empirical evidence of growth in language teachers' practical knowledge in the under-researched context of preservice language teacher education is limited. Informed by both the reflective approach to teaching and an activity theory perspective, this qualitative case study examines what types of classroom practices a group of ESL student teachers learned in practicum experiences, and what pedagogical strategies they appropriated to achieve their learning of those goal-oriented classroom practices. The study is different from the previous teacher reflective thinking studies in that the study participants reflected on their practice teaching experiences, and such reflections were further tested in real-classroom situations and resulted in transformational learning. The results show that the student teachers' learning of effective classroom practices was essentially prompted by reflection of the challenges and dilemmas encountered in the learning-to-teach process. The study points to the importance of foreign and second language teacher preparation programs promoting and sustaining a culture of reflection to empower preservice language teachers to anticipate or cope with the uncertainties and challenges they will encounter in the practicum experience, which is essential to meaningful learning and knowledge construction.