In global trends and current curricular policy reforms in second language (L2) education, there is a great emphasis on repositioning of teachers as assessors and teachers’ role as responsible agents in assessment. However, various factors affect the agency of teachers as assessors in the classroom. This study explored the ways English as a Foreign Language (EFL) teachers perceived the impact of the language assessment teacher education course on their agency as assessors. Likewise, it scrutinized the challenges and opportunities teachers confronted in leveraging the acquired knowledge and skills to enhance their assessment agency and contribute to their overall professional development. As for dataset, this phenomenological study targeted 50 EFL teachers, with 25 participants completing an open-ended questionnaire and the other 25 composing narratives. The research findings, using MAXQDA software (v. 20) for content and thematic analysis, revealed that EFL teachers perceived a significant positive influence of language assessment teacher education courses on their agency as assessors in the classroom. This led to their increased confidence and competence in assessment practices. They found limited institutional support and resources as their main challenges. However, they claimed opportunities would arise from collaborative professional networks and tailored mentoring to effectively apply knowledge and skills gained from language assessment teacher education courses for their professional development. The findings offer valuable implications for language assessment teacher education and professional development initiatives, illuminating the potential predicaments and expediters in enhancing teachers’ assessment agency and fostering their continuous professional growth.