The present study, applied to a sample of preparatory Syrian students, aimed at studying the use of code-switching for students' performance in the classroom and the reasons for using code-switching. Although code-switching has been widely examined in different educational contexts, there is still limited research addressing its impact on English as a Foreign Language (EFL) learners in Syria, especially at the preparatory stage. This lack of empirical evidence has created uncertainty among teachers and policymakers regarding whether code-switching hinders or enhances learning. Thus, the problem this study seeks to address is the absence of clear, context-specific findings on how code-switching influences Syrian students' academic performance and classroom experiences. This experimental study adopts a mixed-methods design, integrating both quantitative and qualitative approaches, using three data collection instruments: tests (pre- and post-), a questionnaire, and interviews. Sixty students participated; they were at eighth grade at preparatory schools in the second semester of the academic year 2024–2025. They were divided into two equal groups: the experimental and the control. The analysis of the data showed that the experimental group outperformed the control group in vocabulary learning, reading comprehension, grammar use, and writing development. It also showed that overcrowded classrooms and time constraints were the main difficulties the participants encountered. However, code-switching was fruitful, as it helped the participants to have better results in their tests. In addition, the results showed that limited code-switching was very important. Moreover, teachers pointed out that they use code-switching to ensure clarity, particularly when introducing new vocabularies and grammar rules. They also use it to manage classrooms and support students' emotional comfort. Code-switching helped students better understand English lessons, reduce confusion, and participate more confidently.