Iran Language Institute (ILI) plays a crucial role in teaching English in Iran and offers a comprehensive Teacher Training Course (TTC) for the teachers before their being employed. Still, these teachers encounter difficulties in different areas, but there are few studies investigating the teaching challenges of EFL teachers teaching at ILI. Thus, this study investigated the teaching challenges of newly-hired and experienced teachers, teaching at different age levels. The data were gathered data through 100 classroom observation forms belonging to 18 kids’ teachers, 47 young-adults’ teachers, and 35 adults’ teachers (69 experienced and 31 newly-hired). We also interviewed with 5 kids’ teachers, 5 young-adults’ teachers, and 6 adults’ teachers. It was revealed that young-adults’ teachers faced fewer challenges than kids’ and adults’ teachers. Besides, experienced teachers encountered fewer problems than newly-hired teachers. The results of the observation forms were different from the interviews. However, time management was the only problem which was mentioned in the interviews, observation forms, and different age levels. According to the teachers, the reason behind these challenges was the intensive syllabus, old books and videos, and teachers’ having to follow a series of fixed teaching steps.
