Recently, the use of language learners' mother tongue, code-switching, alongside English in EFL classrooms has received considerable attention. The main objectives of this study were to present the results of a qualitative study which investigated the types and functions of code-switching at an intermediate English Proficiency level in EFL classrooms. Moreover, gender preferences were investigated. To this end, 50 hours of four class performances were observed, audio-recorded and analyzed to answer the proposed research questions. The results of this study suggested that teachers applied code-switching more frequently when they tried to give Persian equivalents of English words and expressions. It should be pointed out that the application of intersentential code-switching turned out to be more salient among both teachers and students. Code-switching was more frequent while students were carrying out the assigned tasks. Male students switched when they said humorous remarks while their female classmates switched more frequently when they asked and/or gave L1 equivalents. Filling in the attitude questionnaire, the majority of students believed that in several cases neither teachers nor students should apply Persian as much as possible, even though it facilitated their interactions.