This review-specific protocol guides the review of research that informs the What Works Clearinghouse (WWC) Charter Schools topic area. The review-specific protocol is used in conjunction with the "WWC Procedures and Standards Handbook (version 3.0)." This review focuses on charter school interventions in the United States with students in grades PK-12 with a primary focus on student academic achievement and other outcomes. The following research questions guide this review: (1) What is the impact of charter schools on their students' academic achievement in language arts, mathematics, and other subjects, as measured by test scores?; (2) What is the impact of charter schools on their students' other outcomes, including attendance, experience of disciplinary actions (suspensions or expulsions), social-emotional competence, educational attainment (for example, high school graduation, college entry, and degree completion) and earnings in adulthood?; and (3) What is the systemic impact of the expansion of the charter sector in a community on student achievement and educational attainment outcomes for students in traditional public schools?