In 2019, as in previous years, White students outperformed African American, Hispanic, and American Indian/Alaska Natives in a variety of K-12 outcomes (Darling-Hammond, 2007; de Brey et al., 2019; Jacob & Ludwig, 2008; National Education Association, 2015). The urgency of the opportunity/achievement gap is clear, as the current cohort of students under 5 years of age marks a turning point in student population demographics as the first in which 50 percent are part of a minority race or ethnic group (U.S. Census Bureau, 2015). Sociocultural integration (SCI) is included in the frameworks of successful bilingual programs (Howard et al., 2007; Scanlan & Lopez, 2014). SCI considers the dynamics of relationships with oneself and others as being built in the context of one's racial/ethnic, cultural, and linguistic background (Brisk, 2006; Feinauer & Howard, 2014). Acceptance and appreciation of cultural difference is critical for teachers (Bennett, 2003) and a number of pedagogical frameworks center teachers' role of cultural brokerage as a pathway to fostering positive student outcomes (Grant & Sleeter, 2006; Suarez-Orozco & Suarez-Orozco, 2001; Villegas & Lucas, 2002). In this dissertation, I defined sociocultural integration in a teacher-centered way, and explicitly incorporate teachers' racial/ethnic identity development in the evolution of their actions to support SCI. Second, I operationalized this definition and built a scale for measuring SCI using innovative "lived experiences" scenario items according to the Rasch/Guttman Scenario scale development methodology (Ludlow et al., 2020). The SCI Scale for Teachers showed desirable psychometric properties and is well suited to increase use due to ease of interpretability. [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.]