This study examined how in-service teachers transformed professionally and personally as a result of participation in the International Teacher to Teacher Exchange Program (ITTTE). Six teachers, 3 from the U.S. and 3 from Guatemala, were paired. Each pair spent a total of 8 weeks together, in each other's countries, over the course of 2 years. The pairs reciprocated home stays, school engagement, and cultural learning in three cohorts; 2012-2014, 2014-2016, 2016-2018. In 2018, each participant engaged in a structured interview tailored to the ten meaning phases of Mezirow's transformative learning theory (TLT). The data were analyzed deductively, through the application of the ten meaning phases of transformation. The data were also analyzed inductively to determine additional themes of transformation. The deductive findings revealed 5 out of 6 participants experienced full transformative learning. All 3 Guatemalan teachers transformed professionally with new understandings of mathematics pedagogy. Two U.S. teachers transformed personally, one by learning how to be a more caring teacher and the other by overcoming shyness to engage as a relational teacher. The third U.S. teacher adopted the point of view that speaking a second language had value. The inductive analysis revealed emerged themes of learning, language, relationships, and program affecting others as evident in transformed frames of reference, habits of mind and points of view. Due to the range of participation years, latent effects were noted. The ITTTE was shown to influence transformation in teachers' personal and professional development. TLT was effective in revealing participant transformation within the ITTTE.