Although research generally shows that teachers matter for student achievements, it is not clear what attributes make a teacher more successful in enhancing students’ performance. Much of the empirical work has focused on observable teacher characteristics. In this paper, we go further than that. We examine how teacher subject knowledge, pedagogical skill, effective instruction time and classroom teaching practices influence student test scores in maths and language. Results indicate that teachers who spend more time on instruction and can keep student on-task during the lesson are associated with higher student test scores. A number of classroom teaching practices, including the practice of challenging students by asking questions during the lesson, have an effect on student test scores although the effect differs between language and maths.