Authors. Previous research identified a strong correlation between mathematics and science performance albeit for small samples of students. Even though there was a high correlation between mathematics and science performance, researchers examining students' STEM achievement investigated mathematics and science achievement separately. The present study brings science and mathematics objectives together to constitute a higher order STEM assessment model. Data (science and mathematics scores) were gathered from 231,966 students (52% female) who were in 11 th grade and took the state mandated test in 2013. A second-order confirmatory factor analysis was used to create a STEM assessment model. The fit indices showed indicated it was an adequate model fit for the data. However, the lack of assessments of technology and engineering objectives taught in K-12 make estimating the effectiveness of STEM teaching and learning tenable at best.