Students served in alternative and segregated settings tend to receive educational services that are not on par with their public school peers. To develop a better understanding of the problem, the authors conducted a national study of secondary psychiatric schools in the United States. Specifically, the authors administered a survey to mathematics teachers in psychiatric schools to investigate (a) student and classroom level characteristics, and (b) special education mathematics teachers' reported use of research-supported instructional practices with students classified with a learning disability (LD) or emotional/behavioural disorder (ED). The majority of the participating teachers stated that most of their students performed below grade level in mathematics. Teachers also reported frequently using a number of research-supported practices, including components of explicit instruction, strategy instruction, real-world problem solving, and instructional adaptations. However, the respondents also indicated that they seldom or never used a number of other research-supported practices. The authors provide implications for practice and future research based on the findings.