The primary purpose of the present study is to ascertain high school students' perceptions of the efficacy of blended learning in English as a Foreign Language (EFL) classes based on the Education Informatics Network (EIN) which is used as a learning management system in Turkish K-12 schools. The sample of the study was composed of 122 EFL students studying at a state high school. The study was designed with a convergent research design, one of the mixed-methods research designs. Quantitative findings showed that students' general views on EIN-based blended learning were neutral, yet positive about face-to-face lessons. The obtained qualitative findings mostly converged with the quantitative data results, and they clarified that students had both positive and negative opinions about the impact of blended learning on the development of language skills, assessment, learner autonomy, and classroom atmosphere. Furthermore, interview findings indicated that students expected the EIN portal to be free of technical problems, easily accessible and to include more enjoyable and various activities for a better implementation of the EIN-based blended learning. Lastly, several suggestions for further research were put forward as well as some educational implications for teaching EFL in an EIN-based blended learning environment.