The purpose of this correlational study was to examine the impact of employing fully credentialed high school mathematics teachers on students' academic performance. Among the issues affecting high school mathematics education exposed in the literature, the level of teacher qualification in general and credentialing in particular was rarely addressed. This study investigated the issue of teacher qualification, which can be used to construct an institutional and theoretical framework for improvement in mathematics education. The research question asked whether the percentage of credentialed high school teachers in California correlated positively with the mathematics performance of students. The research design involved the tabulation of available data on high school teachers of mathematics and students in 3 large school districts and applying correlation analysis to standardized state-test results and percentage of credentialed teachers. A significant positive correlation indicated that fully credentialed teachers impacted student achievement as measured by mathematics scores on standardized tests. The resulting social change potentially would be significant, from improvement of the United States' global standing in mathematics to savings of reeducation dollars by industry thanks to an increasingly better qualified domestic workforce.