The study finds out the triggers for switching from one language to another in the classrooms at the tertiary level in Bangladesh. It takes a closer look at the spoken discourse in the classroom situations where English is taught as a second language. It examines and presents data on the reasons behind the teachers' and the students' Bangla-English code- switch as well as presenting the percentage of the students' frequency level for code-switching occurring in the classrooms. It also helps to find the fundamental trigger for code-switching. Code- switching is the central issue of bilingual research (Milroy, 1995, p. 7) and the study findings contributes more information on code-switching as well as adding valuable information regarding classroom management techniques, second language acquisition, discourse analysis, and bilingualism.