Black middle school students in the United States continue to perform poorly on standardized reading achievement tests in comparison to other racial and ethnic groups. The purpose of this research study was to examine the effectiveness of a vocabulary-focused test preparation program for Black middle school students. The theoretical framework consisted of Thorndike's concept of test-wiseness, a test-taking capacity. Teachers at the research site were trained on Larry Bell's 12 Powerful Words strategy that aims to make students test-wise, that is, to familiarize them with key vocabulary terms related to tests. An intact-group comparison was conducted, involving a total of N = 679 Black students in Grades 6, 7, and 8 with 370 girls and 309 boys. An analysis of covariance showed significant effects for Grade 6, marginally significant effects for Grade 7, and nonsignificant effects for Grade 8. These findings suggest that the 12 Powerful Words are effective and that their effect decreases with students' age. As a practical consequence, instructional leaders will be able to make more informed decisions regarding test preparation and potentially reduce the number of underperforming students in classrooms.