This study of teacher effectiveness and student achievement in science demonstrated that effective teachers positively impact student learning. A general linear mixed model was used to assess change in student scores on the Discovery Inquiry Test as a function of time, race, teacher effectiveness, gender, and impact of teacher effectiveness in prior years, over a 3-year period. Effective teaching was identified through a series of classroom observations using the Local Systemic Change Classroom Observation Protocol (Horizon Research, 1999). This study found that effective teaching increases student achievement and closes achievement gaps for all students. Findings from this study provide evidence that effective teaching each year may be the key to eliminating achievement gaps in science. © 2006 Wiley Periodicals, Inc. Sci Ed91:371–383, 2007