Teachers’ beliefs about standards-based mathematics curricula can have a direct impact on the implementation of those curricula. Yet, new standards-based curricular approaches, mandated as reform structures under the No Child Left Behind Act (NCLB), fail to account for the beliefs of teachers regarding the curricula in the implementation of new instructional reform practices or policies. The purpose of this quantitative, ex post facto study was to examine pre-existing survey data from a sample (n = 362) of elementary, middle, and high school teachers in an urban school district to analyze the relationship between teachers’ beliefs regarding the use of a standards-based mathematics curriculum and implementation of that curriculum. The theory of planned behavior (TPB), whose proponents posit that beliefs direct behavior, provided the theoretical framework for the study. The three constructs of TPB, attitude, subjective norms, and perceived behavioral control, were used as proxies for the study’s independent variables: teacher beliefs about the curriculum, teacher beliefs about the professional community, and teacher beliefs about instructional leadership. The dependent variable was curriculum implementation. Both descriptive and inferential statistical analyses were used, including Pearson correlations, to analyze data. The findings of this study showed no significant correlation between teacher beliefs and implementation of the curriculum. School districts, school administrators and mathematic teachers will benefit from understanding the value of professional learning communities, positive social norms and perceived behavioral control as factors for promoting collective accountability under NCLB and teacher practice and implementation of standards-based curriculum reform.