This paper presents a research finding which aimed to investigate the perceptions held by High School Students and English language teachers on the characteristics of an Effective English teacher and the effects of these perceptions in learning as well as to compare the perceptions held by the two groups in purposely selected four High Schools found in the Guraghe Zone. In this study, 134 students drawn from two grade levels, namely 9 and 11, and 27 English teachers who teach in those schools were involved as sources of data. The data were collected from the subjects through a five point Likert Scale questionnaire consisting of three categories of teacher effectiveness: English Proficiency (8 items), Pedagogical Knowledge (18 items) and Socio-Affective Skills (18 items). Overall, the students in this study perceived significantly different characteristics from the teachers in all the three categories with the students' high endorsement to Pedagogical Knowledge and the teachers' high ranking to English Proficiency. Both the students and the teachers in this study believed that the effective English language teacher should be able to read, write and speak English well, explain things well, provide interesting activities, arouse students' motivation to learn English well, help students develop self-confidence in order to learn English well, encourage students to try to do their best, set high expectations for students, have positive attitude towards his/her career and the learners and assess what the learners have learned reasonably.