Although Kreyol is the language spoken and understood by the majority of Haitians, French is the language used as the medium for instruction. The use of a foreign language as a means for students to acquire literacy is a practice that has led to an ineffective educational system in Haiti. The aim of the quasi-experimental research study is to study the effects of using Kreyol versus French as the instructional method in math and science classes. Participants were selected from a target population of 246 girls at a private school. Students from this institution are part of the 29% of people who attend secondary schools in Haiti. The 139 students that were part of the sample were randomly divided into two groups per class (standard and Kreyol condition) and were given a pre-test followed by a lesson then a post-test. Students in the standard group were taught in French and those in experimental group in Kreyol. Data gathered from the intervention were analyzed and results indicated that pre-test scores of French condition and Kreyol condition groups were normally distributed. When ANCOVA was used as one of the data analysis tools, because it French conditions for pre-test values and allows for observation of post-test scores, results yielded confirmed a significant difference between the French condition and Kreyol condition groups. The results from this quasi-experimental study provided data that aligned with the literature review and demonstrated that there was in fact a significant difference in performance when Kreyol was used as a medium for instruction instead of French. The results further provide statistical data confirming the important role that Kreyol should play in the improvement of the Haitian education system. [This book was edited by Ismail Sahin and Tami Shelley.]