This study attempted to examine: 1) the professional competencies in English reading comprehension of student teachers before and after instruction using a task-based learning approach combined with graphic organizer techniques, 2) the professional competencies in English writing of student teachers before and after the same instructional method, and 3) the self-assessment of these competencies before and after the intervention. The sample comprised 30 student teachers majoring in Early Childhood Education and Mathematics at the Faculty of Education of a university located in Thailand during the academic year 2023. These participants were obtained through cluster random sampling using sections as the sampling units. The research employed an experimental design, specifically a one-group pretest-posttest design. The experiment began with a pretest, followed by 18 instructional sessions aimed at enhancing the professional competencies in English reading and writing through a task-based learning approach combined with concept graphic organizer techniques. Key research instruments included: 1) three learning units for developing professional competencies, 2) tests measuring these competencies, and 3) self-assessment questionnaires. Data were analyzed using basic statistics, including mean, standard deviation, and paired t-tests. The results revealed that: 1) the professional competency in English reading of student teachers significantly improved after the intervention (p < 0.05), 2) the professional competency in English writing also significantly improved post-intervention (p < .05), and 3) student teachers' self-assessments of their competencies in both English reading and writing were significantly higher after the intervention (p < 0.05).