After the outlawing of the Mexican American Studies (MAS) program in Tucson, Arizona, K-12 Ethnic Studies programs have materialized across the U.S. at an accelerated rate creating an urgent need for critical Ethnic Studies professional development for K-12 educators. In direct response to both the elimination of the MAS program and the pressing need for teacher training, the Xicanx Institute for Teaching & Organizing (XITO) emerged as a strategy to continue the legacy of the MAS program. XITO, a grassroots urban education collective, has developed a decolonizing and re-humanizing model of Ethnic Studies professional development to counter the deficit model of current teacher education by infusing critical identity work--a critical analysis of race, power, and systems of oppression--together with an Indigenous epistemological framework formerly implemented in the highly successful MAS program. A thorough description of the philosophy and model of XITO's praxis is presented along with testimonios from participants of the professional development and how they have integrated this critical Ethnic Studies training into their own educational spaces. Recognizing the rate of expansion of K-12 Ethnic Studies programs in the U.S., coalition-building with other grassroots urban education collectives is necessary to scale up the movement to prepare critically and politically conscious Ethnic Studies teachers and organizers.