Non-suicidal self-injury (NSSI), the immediate and deliberate destruction of one's own body tissue, without suicidal intent, and not for purposes that are socially accepted, is a critical concern for youth in schools. Despite significant scholarly advances and increasing clinical awareness of NSSI, many school mental health professionals (MHPs) continue to report feeling ill equipped to support students who self-injure, and emphasize a need for formal education about NSSI and its management in schools. Thus, the first part of this article summarizes current NSSI research on prevalence, age of onset, gender differences, functions, risk factors, and associations with suicide. Emerging from this review, the second part offers research-informed recommendations for MHPs managing NSSI in schools, including guidelines for (a) identifying students at elevated risk of self-injury, (b) developing a protocol for school personnel's initial response to student self-injury, (c) first-level assessment of NSSI, and (d) managing critical issues related to NSSI contagion and online activity.