The field of education of deaf and hard of hearing (DHH) students has a paucity of evidence-based practices (EBPs) to guide instruction. The authors discussed how the research methodology of single-case design (SCD) can be used to build EBPs through direct and systematic replication of studies. An overview of SCD research methods is presented, including an explanation of how internal and external validity issues are addressed, and why SCD is appropriate for intervention research with DHH children. The authors then examine the SCD research in the field according to quality indicators (QIs; at the individual level and as a body of evidence) to determine the existing evidence base. Finally, future replication areas are recommended to fill the gaps in SCD research with students who are DHH in order to add to the evidence base in the field.