The authors assessed the quality of single-case design (SCD) studies that assess the impact of interventions on outcomes for individuals who are deaf or hard-of-hearing (DHH). More specifically, the What Works Clearinghouse (WWC) standards for SCD research were used to assess design quality and the strength of evidence of peer-reviewed studies available in the peer-reviewed, published literature. The analysis yielded four studies that met the WWC standards for design quality, of which two demonstrated moderate to strong evidence for efficacy of the studied intervention. Results of this review are discussed in light of the benefits and the challenges to applying the WWC design standards to research with DHH individuals and other diverse, low-incidence populations.