This study examines a Technology, Pedagogy, Content Knowledge (TPACK) training framework for pre- and in-service mathematics teachers that enables them to experience inquiry-based learning as learners in a dynamic geometry environment that serves as a mathematics laboratory. We investigate the effect of this experience on the teachers' TPACK, based on both their perceptions towards implementing technology into their teaching; and on their TPACK level demonstrated in inquiry-based dynamic geometry activities they designed for instructional purposes. We present a rubric for assessing teachers' TPACK level through inquiry-based dynamic geometry activities after they practiced in the mathematics lab. Our findings reveal a significant positive change in the participants' perceived TPACK, from pre-to post-intervention, only for factors that relate to the technology component and its integration with the pedagogy and content components. In the activities designed by participants, technology was more content-oriented than inquiry-oriented. No difference was found between the two participating groups in the ability to design dynamic geometry activities after they practiced in the mathematics lab. The study suggests theoretical, practical, and methodological contributions related to conceptualizing TPACK in the context of a mathematics lab and to designing TPACK training frameworks for pre- and in-service teachers.