This guide is designed to support the development of mathematics proficiency for youth in short-term juvenile correctional facilities. Mathematics proficiency includes mastery and fluency in foundational numeracy; an understanding of complex, grade-appropriate concepts and procedures; and application of those competencies to solve relevant, real-life problems. It is primarily designed to help practitioners implement research-based, effective mathematics instruction in short-term facilities, defined as institutions that typically house youth detained in juvenile corrections or other residential facilities for periods of 90 days or less. A secondary audience includes local juvenile justice facilities program coordinators, facility administrators, and state Title I, Part D, coordinators. This guide provides recommendations, strategies, and examples for teachers that increase the likelihood that students will become more proficient at understanding mathematics and applying existing and emerging skills. Just as important, the guide can help teachers promote the self-confidence of students in their ability to use mathematics to solve problems. An annotated bibliography is included.