A systematic review explored the evidence base of literacy intervention studies that examined the early years of schooling (preschool through first grade) of participants who were d/Deaf or hard of hearing (d/Dhh). Specific inclusion criteria were used to select single-case design (SCD) studies published in peer-reviewed journals between 2004 and 2017. Fourteen studies met the criteria. Studies were evaluated according to the quality indicators for evidence-based research, individually and across studies (Horner et al., 2005; Institute for Educational Sciences, 2017; Kratochwill et al., 2013). Five of the 14 studies were categorized as "Meets Standards Without Reservations"; 7 as "Meets Standards With Reservations"; and 2 as "Does Not Meet Standards." None met the established criteria for an evidence base. Recommendations for future research are provided, with specific studies highlighted for replication to build evidence-based practices using SCD in the field of educating students who are d/Dhh.