A majority of students at the local University College of Science and Education (UCSE, pseudonym) in Jamaica do not have the conceptual understanding of mathematical principles to function in a competitive and highly globalized marketplace. In 2013 and 2014, 88% and 92% of freshmen education students scored at the lowest 2 levels on the Mathematics Diagnostic Test (MDT). The instructional language at UCSE is Standard English (SE) whereas most students speak Jamaican dialect (JD). The purpose of this study was to determine the effect that the language of instruction has on student achievement in math as measured by the MDT. Guided by Vygotsky's social development theory, the research questions focused on comparing MDT change scores between students who were taught using JD and those using SE as the instructional language. The quasi-experimental design used ex post facto data including pretest and posttest MDT scores from 40 freshmen of whom 20 were instructed in JD and 20 in SE. The results of an independent sample t test showed that the difference in the MDT change score was significant. The JD students had a higher improvement score. Consequently, it is recommended that math instructors use JD to instruct freshmen education students whose native language is JD. A professional development session for math teachers was created that demonstrates how to teach in JD while simultaneously scaffolding the instruction in a way that students can learn SE and be prepared for the following year at UCSE. If students understand the math concepts in their freshman year, they are more likely to continue their college education and to become productive members of Jamaica's economy which is dependent on employees that are proficient in math.