This paper reports on research findings on leaner-centered approach compared to teacher-centered approach in teaching English grammar as a foreign language in Iranian high school context. It shows the need for grammar instruction in English language classes when roughly all education efforts are bottom-up explicit approach. One could compare and contrast these two learning approaches and try to evaluate the effectiveness of them. To this end, a cohort of 60 male homogeneous students at a junior high school in Tabriz, Iran participated in this study. All participants were native speakers of Azerbaijani and Persian aged around 16. There were two classes, including 30 students in each group (class) who were assigned to the control and experimental group. The experimental group received a treatment in passive-active voice, followed by a grammar pre- and post-test. All the tests consisted of multiple-choice, cloze, and fill-in-blanks, which were administered to study the homogeneity in their grammar knowledge over one month, and the results were compared. Two groups were observed, namely the control group (group A) or teacher-centered and the experimental group (group B) or student-centered. This experimental study also comprised classroom observations and teacher interview. When the students are given the opportunity to merge input in what they learn and how they learn, academic achievements and comprehension occur. The results support the implementation of teacher-centered process for the purpose of developing grammar knowledge of Iranian EFL learners. English classes cannot fulfill the learners’ needs on communication. The findings suggest the need for explicit teaching of grammar rules and their use through communicative tasks.