The authors report on a study aimed at exploring the role of a teacher education program (TEP) rested upon the tenets of critical pedagogy in influencing teachers' cognitions and practices concerning first-language (L1) use in second-language (L2) classrooms. Participants were 10 Iranian English as a foreign language teachers, whose cognitions were tapped into by means of semistructured interviews and stimulated recall sessions before and after the TEP. Two sessions of each teacher's practice which were regularly audio- and video-recorded by the institutes were obtained, transcribed, and analyzed to measure their amount of L1 use. Results of the study indicated that before the TEP, most of the teachers held negative attitudes toward L1, rarely used L1, and also discouraged their students from switching to it. However, after the TEP, it was found that they reconsidered their cognitive-oriented views, incorporated affective factors into their decision-making processes, and expressed more positive attitudes to L1 use. Moreover, they showed more tendencies to make use of it on the actual level of their classrooms. The authors conclude with discussing the findings, presenting some pedagogical implications for pertinent stakeholders, and sketching out some areas for further research.