This study investigates code-switching among EFL students during pair work in uppersecondary school classroom settings. The aim is to uncover the reasons behind code-switchingand the factors influencing code-switching. Using a mixed-methods approach, the research usesclassroom observations and survey to collect data from 13 EFL students. Observations captured real-time code-switching instances, while the survey gathered students' perceptions and self-reported motivations for code-switching. The findings reveal that the most frequent reason for code-switching is a lack of vocabulary, both observed in the classrooms and reported by thestudents themselves. The second most frequent observed reason for code-switching is the needfor clarifications or explanations in Swedish. In students' self-reports, difficulty remembering English words was the second most common reason. Lastly, engaging in miscellaneous talkemerged as the third most common reason observed in classroom interactions, while studentsreported that code-switching occurs naturally or comes as a reflex as their third most commonreason in the questionnaire. The findings indicate that code-switching serves as a strategic toolto manage linguistic gaps, maintain conversational flow and express emotions, among otherthings.