This study investigates ChatGPT's efficacy in fostering autonomous ESP writing development across different proficiency levels, while identifying its strengths and limitations in enhancing specific writing competencies. A quasi-experimental pretest-posttest design was employed with 176 Saudi university students (A1-B1 proficiency) over 8 weeks. Standardized email-writing assessments measured progress in Content, Format/Structure, Grammar/Punctuation, and Clarity/Cohesion, with ANOVA and effect size analyses determining significant changes. Results showed significant improvements (p.05). The model explained 57-74% of variance (R²), with strongest effects for A1 learners. This study provides the first empirical evidence of ChatGPT's proficiency-dependent effectiveness in ESP writing, establishing (1) clear thresholds for AI's optimal utility across skill levels, (2) critical limitations in developing higher-order writing skills, and (3) a foundation for blended AI-human writing pedagogy in ESP contexts.
Mohamed et al. (2025) studied this question.