Cognitive/Academic Language Proficiency (CALP) is a construct developed by linguists that distinguishes everyday conversational language and language used in literature and on academic tests. The "No Child Left Behind Act" has created impetus for scientifically researched pedagogy that serves to increase academic achievement of groups who have been historically marginalized. Lack of CALP was identified as one factor that may prevent academic advancement among certain populations. An experiment was performed to demonstrate a causal relationship between increased CALP and improved Ohio Proficiency Test Scores. Twenty-three low-achieving sixth grade students, six of whom had IEPs, received an eight-week treatment program to improve their cognitive/academic language. Pre-and post-tests assessed changes in proficiency test scores. Differences in scores were statistically analyzed. Scores showed a significant positive treatment effect for students not on IEPs. The development of cognitive/academic language shows promise as a method for improving the proficiency test scores of low-achieving students. [This thesis was presented in partial fulfillment of the requirements for the Degree of Masters of Education.]