The purpose of this non-experimental quantitative study was to investigate the relationship between Pennsylvania's Classroom Diagnostic Tools (CDT) interim assessments and the state-mandated Pennsylvania System of School Assessment (PSSA) and to create linear regression equations that could be used as models to predict student performance on the PSSA assessments. It was not known to what degree CDT assessment scores could be used to predict PSSA performance. A review of literature showed that no studies could be found which investigated if CDT scores could be used to predict PSSA performance and revealed that a gap in research exists on how well interim pretests and posttests can predict performance on state-mandated assessments. This study used student scaled scores from two rounds of CDT testing in literacy and mathematics, which were administered during the 2015-2016 school year and PSSA scores in language arts and mathematics from the 2016 test administration. The sample consisted of 760 students in sixth, seventh, and eighth grade from a middle school located in southeastern Pennsylvania. Pearson product-moment correlation and linear regression analysis were calculated to investigate the relationship between first round and second round CDT assessment scores in literacy and mathematics and PSSA assessment scores in language arts and mathematics. Pearson product-moment correlation was also calculated to investigate the relationship between CDT and PSSA assessment scores for black, economically disadvantaged, and special education subgroups. The results showed that strong to very strong correlations existed between both rounds of CDT assessment scores in literacy and mathematics and PSSA assessment scores in language arts and mathematics for sixth, seventh, and eighth grade. The results also indicated that a positive linear relationship existed between CDT and PSSA scores in both content areas for sixth, seventh, and eighth grade. The results showed that stronger correlations existed for the black, economically disadvantaged, and special education subgroups. The overall findings indicated that a strong predictive relationship existed between CDT assessment scores and PSSA assessment scores. The formula Y = a + bX, was used to develop linear regression equations for each grade level and content area. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone 1-800-521-0600. Web page: http://www.proquest.com/en-US/products/dissertations/individuals.shtml.]