xvi, 216 p. A print copy of this thesis is available through the UO Libraries. Search the library catalog for the location and call number. / The primary purpose of this study was to design and validate a measure of teacher knowledge of Universal Design for Assessment (TK-UDA). Guided by a validity framework, a number of inferences, assumptions, and evidences supported this investigation. By addressing a series of research questions, evidence was garnered for the use of the measure to describe what teachers know about assessment accessibility issues through their application of seven UDA principles. The investigation used research designs and sampling procedures specific to each research question. The TK-UDA was designed to capture depth of knowledge, from background to declarative to applied, through a variety of item types. Internal, external, and teacher reviews provided evidence to support the content validity of the measure, and, based on the feedback from these reviews, the measure was revised to improve content and clarity. The measure was then implemented online; a purposeful sample of experts and inservice and preservice teachers was invited to participate in the study. It was anticipated that these participants would represent a range of knowledge of UDA. Following measure implementation, analyses were conducted to evaluate whether performance on items accurately reflected a continuum of teacher knowledge. Evidence of discriminant/criterion-related validity was examined by evaluating group differences. Based on results from t -tests and MANOVAs, no significant differences between groups (based on level of expertise) were found. Item Response Theory (IRT) scaling of items along a continuum indicated that declarative knowledge items were generally less difficult than applied knowledge items. IRT scaling of person scores represented a rather narrow range of knowledge within the sample. Reliability estimates from the IRT scaling and test-retest indicated strong item reliability, relatively weak person reliability, and satisfactory test-retest reliability, respectively. To obtain evidence regarding the usefulness of the measure to determine professional development needs, a Kruskal-Wallis rank-order test was conducted to evaluate the differential difficulty of UDA elements within the applied knowledge section. This provided initial evidence for identifying professional development needs at the element level. These results provide information that will guide further instrument development and future research in this area. / Committee in charge: Paul Yovanoff, Chairperson, Educational Methodology, Policy, and Leadership; Elizabeth Ham, Member, Special Education and Clinical Sciences; Leanne Ketterlin Geller, Member, Educational Methodology, Policy, and Leadership; Douglas Blandy, Outside Member, Arts and Administration