Demographics in the United States are rapidly changing. It is projected that by the year 2050, the minority population of the country will instead be the majority (Craig & Richeson, 2017), and according to the Pew Research Center (2019), in some areas of the country, this is already the case. With changing demographics in the United States resulting in minority-majority schools, high school teachers are not prepared and lack the knowledge, skills, and dispositions required to teach through a culturally responsive lens (Mosconi, 2022). Teacher preparation programs do not effectively support teachers in building their capacity to integrate culturally sustaining pedagogies into their instructional practices (Harper, 2017). The purpose of this qualitative Heideggerian phenomenological study is to explore the experiences of teachers during their teacher preparation programs to understand the training and preparation they received to integrate culturally sustaining practices (CSP) into their instruction. Understanding how K-12 Teacher Preparation Program Standards affect the effectiveness of new teachers in the classroom is crucial to ensure that proper training is provided and that all students succeed. One focus group and three semi-structured interviews were conducted to capture teacher's perceptions and experiences of teacher preparation programs and their current ability to be equity-minded educators with the ability to serve ethnically, culturally, and linguistically diverse learners. Three overarching research questions guided this study: (1) How do high school teachers describe their teacher preparation programs' impact on their preparedness to utilize culturally sustaining pedagogies? (2) How do high school teachers describe the ways that in-service professional development has been used to build their knowledge gaps surrounding culturally sustaining pedagogies? (3) What do high school teachers share as ways that teacher preparation programs and in-service professional development can be improved to support teachers' capacity to serve ethnically, culturally, and linguistically diverse learners? The researcher conducted one-on-one and a focus group interview. The major themes included the lack of CSP training in Teacher Preparation Programs and in Local Educational Agencies, the unintentional CSP field training experiences, and CSP challenges at LEAs. [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.]