Current teaching standards and practices are dictated, at least in part, by state- and district-mandated standardized tests. Yet, despite being surrounded by data, teachers receive only basic trainings on how to use assessments. In reality, teachers use data and assessments daily--even minute by minute--through the assessment process, which uses multiple data sources to make informed decisions on student learning and teaching practices. A measure was needed to understand how the policies and expectations from schools, districts, and states compare with actual classroom practices. The teachers Knowledge and Use of Data and Assessment (tKUDA) measure was designed to do just that. This study sought to create and assess the validity of the tKUDA while exploring differences between respondents and relationships between factors. The tKUDA is a tool with support for reliability and validity to be used to gauge teacher practice around data and assessments through the assessment process. Reliability was assessed via Cronbach's alpha (Knowledge factor alpha = 0.95, Use factor alpha = 0.96) and using item response theory (Knowledge person separation = 2.52, reliability of person separation = 0.86; Use person separation = 1.11, reliability of person separation = 0.55). Validity was evidenced through correlations between expert interview ratings and item difficulty (r = 0.87), correlations between similar, known measures and the tKUDA (r = 0.41). Additionally, construct validity was seen through scale use and internal validity was presented using differential item function. The tKUDA allows administration, university teacher preparation programs, and researchers to identify strengths and needs of teachers in order to create meaningful, targeted training opportunities. Differences were seen between Knowledge and Years of Teaching and between Use and Content Expertise. A moderate, positive relationship between Knowledge and Use was found with Knowledge explaining 22% of Use. Evidence for possible differences in this relationship by content are also noticed and discussed. [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.bibliotheek.ehb.be/en-US/products/dissertations/individuals.shtml.]