This report provides evidence of the substantive and structural validity of the Knowledge for Teaching Elementary Fractions Test. Field-test data were gathered with a sample of 241 elementary educators, including teachers, administrators, and instructional support personnel, in spring 2017, as part of a larger study involving a multisite cluster-randomized trial evaluation design to investigate the effects of lesson study and a fractions resource toolkit on classroom instruction and student achievement in fractions. The web-based test was designed to measure mathematical knowledge for teaching (MKT) in the domain of fractions at the elementary level. We found that the Knowledge for Teaching Elementary Fractions test measures a dominant factor, supporting unidimensionality in the data. The purpose, or intended use, of the Knowledge for Teaching Elementary Fractions (K-TEF) test data gathered in spring 2017 is to produce ability estimates that can be used to serve as the dependent variable in models estimating the effect of the intervention on teacher MKT, as well as to investigate MKT as a potential mediator of the effect of the program on students. Reliability, test-information, and item-discrimination estimates appear to fit the intended purpose of the test.