Multi-grade teaching has been considered as a solution in the education system to provide access to basic education and make education accessible to all. This research aims to identify the challenges faced by elementary school teachers in multi-grade elementary school classrooms. This research is qualitative and grounded theory in nature. The statistical population of the present study consists of all teachers and head teachers working in multi-grade classes in Sareyn city, who were teaching in multi-grade classes in the academic year 1401-1402. Of these, 13 people were selected as participants in a purposeful and accessible manner and until data saturation was reached. The data were collected using semi-structured interviews and analyzed using MAXQDA 2020 software. Its validity was confirmed by the method of interviewing experts, by the method of time stability and its reliability by the method of member review and interviewing experts. Its validity was confirmed by the method of expert review and by the method of member review and interviewing experts. Its reliability was calculated by the method of agreement between two coders. Analysis of the data identified 15 categories and 42 codes. The identified categories are: Causal factors (teacher's educational weakness, high content of books, lack of educational technology, lack of educational time, weakness of courses and workshops, lack of teacher experience), background factors (cultural challenges, inappropriate age and gender composition, lack of space, financial affairs, management affairs, classroom space), intervening factors (travel problems, inappropriate IQ composition, parent-related matters).