The deployment of increasing numbers of teacher assistants (TAs) to support students, especially those with disabilities or other special needs, presumably has been perpetuated with benevolent intentions meant to help both students and teachers. Given the contemporary emphasis on theoretically grounded and evidenced-based approaches in education, this author finds it interesting and somewhat perplexing that teacher assistant utilization has advanced steadily and their roles have expanded instructionally despite lacking both a theoretically defensible foundation and a substantive evidence base. Literature reviews on teacher assistants in special education in the United States (called paraprofessionals in US federal law) have reported an overall paucity of data and corresponding lack of evidence attesting to the efficacy of paraprofessionals enhancing student outcomes, and no literature to date has offered a compelling rationale in support of assigning the least qualified school personnel, namely teacher assistants, to students with the most complex learning challenges. Data collected by the Deployment and Impact of Support Staff (DISS) project represents a substantial and unique contribution to the research literature on the utilization and impact of teacher assistants given its large scope, longitudinal nature, multiple data collection methods, and focus on the relationships between teacher assistant deployment and student achievement. In doing so, it challenges the status quo and offers insights to guide school improvement. This commentary, based on a subset of DISS project data presented in this issue (Webster et al. 2010), describes: (1) findings that replicate existing data collected in US schools; (2) substantially new findings that extend the field's research base; and (3) implications for policy and practice. (Contains 1 table.)