In support of the national movement to improve mathematics instruction and assessment, states and districts are looking for the best tools to measure student progress toward proficiency. There is a national dialogue about how to use 8th-grade measurements like ACT EXPLORE and NAEP as predictors of student success and school accountability. This dissertation shares research that examined alignment of district and national assessments to the 8th-grade Common Core State Standards in Mathematics (CCSSM). Three research questions were examined in this study to determine the extent of content validity and mathematical practice representation in three 8th-grade assessments compared to the CCSSM. The three assessments were: the ACT EXPLORE, the 2009 NAEP released mathematics items, and the Jefferson County Public School (JCPS) district interim assessments. The study utilized a mixed methods research design to answer the three research questions. To determine the extent of content validity in application to the 8th-grade CCSSM content standards, a quantitative principal component analysis to determine domains represented by assessment items was performed on the JCPS interim assessments and the ACT EXPLORE. Qualitative alignment data were gathered from the three assessments utilizing the Webb Alignment Tool (WAT), which also resulted in quantified data. To analyze the representation of the mathematical practices in the three assessments, the researcher used a method similar to that identified in the WAT to determine which practices each assessment item included. Thus, the mathematical practices were analyzed utilizing both qualitative and quantitative data and also included a meeting with content experts to discuss results of the data gathered. Findings of the study indicated that the JCPS interim assessments were considered well aligned to the 8th-grade CCSSM content standards. However, the ACT EXPLORE and 2009 NAEP released items did not align with the 8th-grade CCSSM. Further analyses of the two national exams revealed a higher level of alignment with the 7th-grade CCSSM content but warrant further analysis. Due to a lack of methodological support for identifying the mathematical practices, no results were reported regarding the level of representation of the practices in each of the assessments. [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 (800) 1-800-521-0600. Web page: http://www.proquest.com/en-US/products/dissertations/individuals.shtml.]