This study aims to explore three elementary teacher-researchers’ development, specifically how they grew individually as teacher-researchers, in what aspects they developed, and what factors instigated their development. The three teacher-researchers with experiences in research were enrolled in the doctoral seminar that the researcher taught for a semester. The data included each participant’s pre- and post-surveys, reflection e-journal, final portfolio, final paper as well as the researcher’s field notes. Based on the narrative inquiry, the data were analyzed qualitatively using content analysis. The major findings are as follows: First, three teacher-researchers grew by interconnecting teaching and research and making efforts to overcome difficulties conducting research. Second, the teacher-researchers developed in terms of cognitive (teacher knowledge and beliefs), affective (teacher motivation and confidence), and metacognitive aspects (teacher reflection and plans). Third, the factors that influenced the teacher-researchers’ development included mediation by activities in the graduate seminar, integration between teaching and research as well as the teacher-researchers’ willingness and aspiration toward teaching and research. It was suggested that teacher education programs need to support teacher-researchers for their professional development more effectively. Further important implications regarding development for English teachers and English teacher-researchers were discussed.