AI-assisted instruction can be applied to diverse contexts and areas in language teaching, aiming to improve different skills, sub-skills and components of language proficiency. The aim of this study was to investigate and compare the effectiveness of AI-assisted instruction in an academic writing course and for vocabulary development in an ESP course at Ilam University, Iran. To this end, following a general proficiency test and two course-specific subject-related placement tests, 32 MA students of TEFL enrolling in the academic writing course were allocated to two homogeneous classes of 16 students, and another 32 MA students of TEFL enrolling in an ESP course for linguistics were allocated to two homogeneous classes of equal size. Both classes in each pair had an equal number of students with high and mid-level general and subject-specific proficiency. In each pair, one class received traditional instruction and the other received AI- assisted instruction, while other factors, such as sessions’ length, frequency, and other aspects of teaching methodology were identical. In the AI-assisted academic writing class, ChatGPT and Microsoft Copilot chatbots were used for providing feedback, revision guidance and tips for outlining, moves and paragraph organization. In the ESP class, AI-assisted vocabulary instruction involved prompting and querying the two chatbots for word grouping, mnemonics building, synonyms, antonyms, related terms and definitions. At the completion of the courses, the students in the writing classes submitted papers rated by three raters in a double-blind manner, and the students in the ESP classes took an achievement test. Ratings, test results and the results of the entrance level tests were analyzed using SPSS software. The statistical analysis consisted of using ANCOVA and paired t-test. Analysis results showed that although in both courses, students of the AI-assisted class outperformed those in the traditional class, the students of the AI-assisted academic writing class benefited more from the use of AI chatbots than those in the ESP class. Effectiveness of AI-assisted instruction in academic writing and vocabulary teaching was confirmed, with a higher level of effectiveness for instruction of academic writing. Further studies are called for with regard to different skills, sub-skills, and components, and concerning the effects of students’ individual differences in different contexts and settings using various AI-powered tools and solutions. Deeper understanding and further insight on levels of effectiveness of AI-based tools in different contexts and settings and for different purposes can help with planning and designing effective AI-assisted courses and programs.
