The easyCBM© CCSS Math tests were developed to help inform teachers' instructional decisions by providing relevant information on students' mathematical skills, relative to the Common Core State Standards (CCSS). This technical report describes a study to explore the validity of the easyCBM© CCSS Math tests by evaluating the relation between students' scores on these measures in Grades 6-8, and the Stanford Achievement Test, 10th edition (SAT-10). High correlations between the two would provide evidence for the validity of the easyCBM© CCSS Math Measures, while a low relation would provide evidence that the measures are targeting different constructs and/or functioning differently. We explore the relation between the measures using both correlational and regression analyses. Results suggest a high relation between the measures, adding to the validity evidence for the easyCBM© CCSS Math measures.