This special issue of "School Psychology Review," entitled "Closing in on Discipline Disproportionality" examined promising approaches and critical issues related to the challenge of closing racial and ethnic gaps in schools' use of exclusionary and punitive discipline practices. In this introductory paper, we briefly reviewed the rationale for and urgency for a focus on disproportionality in discipline and highlighted some of the most salient findings from the five empirical studies in this special issue. We identified some challenges for the field going forward, with particular attention to issues of measurement and structural factors that shape differential disciplinary outcomes. Consistent with the National Association of School Psychologists' (2013) position statement, we emphasized the need to build the science of discipline disparities intervention through more systematic empirical research. Taken together, these new directions are intended to catalyze scientific rigor in the next generation of evidence-based interventions to close the discipline gap. [This paper was published in "School Psychology Review" v47 n2 p109-117 2018.]