La Prueba Maya is a new computer-based diagnostic assessment that was developed to measure the Maya proficiency of Mexican teachers. To assess Mayan fluency in reading, listening, speaking, and writing, La Prueba Maya's battery of tests was taken by 2,507 preschool and primary school teachers in Mexico. Results were used to determine proficiency in Maya as a second language for teachers wishing to work with indigenous Maya-speaking children in Yucatán, Campeche, and Quintana Roo. We ground this work in the theories and research from the fields of anthropology, education, linguistics, second language acquisition, the unique features of indigenous languages, and best practices in language assessment. The results of the tests indicate that the listening test was the easiest for test takers and the written test was the hardest. There are challenges and limitations of testing teachers of indigenous children, particularly when the teachers, in most cases, are new to basic and general testing procedures and digital media. Results of the test pilot showed teachers’ scores were higher in listening and speaking. If Mexico wants to protect heritage languages, then its teachers must be given opportunities to attend to their own competencies in reading and writing to pass the indigenous languages to the next generation.