The study investigated the extent to which teachers who practiced action research changed in light of the new knowledge they gained from their research. A mix of qualitative and quantitative data were collected using a questionnaire, interviews, and focus group discussions from teachers of English as a foreign language at three Ethiopian public universities. The results showed that the teachers who did action research gained knowledge and skills for the betterment of themselves and their practices in various ways. The instrumental role of action research for enhancing the teachers' learning experiences, knowledge, skills, thinking, and teaching practices, as well as their students' learning, were highly valued by the teachers. A Pearson's correlation analysis showed there was a positive association between the teachers' actual practice of action research and their change (r = 0.38, P < 0.025). Action research and change progressed in the same direction. As the P-value was low (< 5%), the influence of chance was unlikely, and the obtained correlation coefficient was statistically significant. The results imply that action research as a practical philosophy of teachers is a powerful tool for personal and professional development for those who engage in the process and who have a stake in the results. This calls for revitalizing action research as part of teaching and learning, wherein teachers are empowered and committed to take initiative and base their teaching on action research results for the purpose of transforming themselves, their practices, and their learners.