International Journal of Research in English Education

en Pitfalls of a Second Language Writer and AI Detection: Evaluating Plagiarism Checking Tools in Iranian EFL Students' Academic Writings Pitfalls of a Second Language Writer and AI Detection: Evaluating Plagiarism Checking Tools in Iranian EFL Students' Academic Writings عمومى General پژوهشي Research obective: This study evaluated AI detection tools’ efficacy in assessing EFL students’ writing, focusing on distinguishing AI-generated from human text without misclassifying L2 work. Methods: A two-phase quantitative design was used. Phase 1 involved 30 BA students from Yazd University producing one non-AI and one ChatGPT-assisted essay on identical topics. Phase 2 compared two MA thesis corpora: 30 from the pre-AI era (2010–2015) and 30 from the post-AI era (2020–2025). All texts were analyzed using Turnitin and Grammarly Premium. Results: Results, analyzed via Wilcoxon Signed-Rank Tests and one-sample t-tests, revealed significant performance divergence. Turnitin demonstrated near-perfect accuracy in identifying AI-assisted essays, whereas Grammarly showed a statistically significant false negative rate, failing to detect some AI content. Both tools accurately analyzed short, human-written essays. However, the thesis analysis revealed increased AI-detection scores in the post-AI corpus, contrasting with near-zero scores in the pre-AI corpus. Conclusion: This finding suggests either actual, undisclosed AI use or algorithmic bias misclassifying Iranian EFL linguistic patterns as AI-generated. The study concludes that while Turnitin is more robust than Grammarly, uncritical tool application risks systematic misjudgment against L2 writers. False positives and negatives threaten academic equity. Thus, AI-detection outputs should trigger pedagogical dialogue and human-led investigation rather than serving as sole misconduct evidence.   ,AI detection tools,Iranian EFL students,false negatives,false positives,plagiarism 70 79 http://ijreeonline.com/browse.php?a_code=A-10-1133-2&slc_lang=en&sid=1 Mohammad Amin Dehghan Baghi Mohammad Amin Dehghan Baghi aminnima@gmail.com 10031947532846004107 10031947532846004107 No Department of English Language and Literature, Faculty of Foreign Language, Yazd University, Yazd, Iran. Department of English Language and Literature, Faculty of Foreign Language, Yazd University, Yazd, Iran. Seyedeh Elham Elhambakhsh Seyedeh Elham Elhambakhsh s.e.elhambakhsh@yazd.ac.ir 10031947532846004108 10031947532846004108 Yes Department of English Language and Literature, Faculty of Foreign Language, Yazd University, Yazd, Iran. Department of English Language and Literature, Faculty of Foreign Language, Yazd University, Yazd, Iran. Ali Mohammad Fazilatfar Ali Mohammad Fazilatfar afazilatfar@yazd.ac.ir 10031947532846004109 10031947532846004109 No Department of English Language and Literature, Faculty of Foreign Language, Yazd University, Yazd, Iran. Department of English Language and Literature, Faculty of Foreign Language, Yazd University, Yazd, Iran.