Abstract
Foreign English teachers in Vietnam play an important role in English language education, yet limited empirical evidence explains how professional development, research competence, and pedagogical competence relate to their English language proficiency. This study examined the relationships among these teacher competencies and determined their predictive effects on English language proficiency. A quantitative quasi-descriptive correlational and causal-comparative design was employed. Using stratified random and proportionate sampling, 140 foreign English teachers were selected from accessible English training centers across major provinces and cities in Vietnam. Data were collected through a validated and pilot-tested self-assessment questionnaire measuring professional development, research competence, and pedagogical competence, together with an adapted English language proficiency test. After obtaining the necessary permissions, the instruments were administered through an online survey platform. The data were analyzed using descriptive statistics, correlation, regression, and factor analysis, including structural equation modeling. The findings showed that pedagogical competence had the strongest positive relationship with and predictive effect on English language proficiency, while research competence and professional development demonstrated comparatively weaker direct effects. The structural model further identified pedagogical competence as the most significant predictor of English language proficiency among the variables examined. These findings suggest that although professional development and research competence remain important dimensions of teacher development, effective teaching strategies, classroom management, instructional planning, and other pedagogical skills are particularly important in supporting teachers' language proficiency. The study concludes that professional development programs for foreign English teachers should place greater emphasis on targeted pedagogical training while maintaining opportunities for research engagement and continuous professional learning. Such programs may contribute to strengthening teacher competencies and improving the quality of English language instruction in Vietnam.