The role of standardized tests in general and college admission tests in particular is a hot topic for educators, administrators and others evaluating the outcomes of educational institutions. The importance of the test scores for both students and institutions is acknowledged, and the test preparation industry has spawned into a multi-billion dollar enterprise. Yet, objective evidence supporting the effectiveness of coaching for college preparatory tests, including the ACT, is virtually nonexistent. This study investigated the effectiveness of a four-week, 20-hour ACT coaching class offered at a large Midwestern high school. The results of this study show that students who participated in the coaching class increased their composite ACT score by 1.5 points over their previous highest ACT composite score. A comparable group at the same high school who did not participate in the coaching achieved an increase of 0.65 points, indicating an effect of coaching of 0.85 points. (Contains 5 tables.)