This study describes a systematic review and synthesis of high-quality intervention research for Grade K-12 students with or at risk for reading difficulties and co-occurring attention-deficit/hyperactivity disorder (SWRD+ADHD) to identify (a) the literature base for high-quality single-case design studies for SWRD+ADHD in grades K-12, (b) the student, study, and intervention characteristics of these studies, (c) the effects of these interventions on reading and behavior outcomes, and (d) the collateral impact of reading interventions and behavior interventions on behavior outcomes and reading outcomes, respectively. Our search and screening process yielded 14 eligible studies published between 1975 to 2021. Five studies implemented a reading intervention, seven studies implemented a behavior support intervention, and two studies implemented a combined reading with behavior support intervention. Tau-U effect sizes ranged from -1.20 to 1.00 for reading inventions and from 0.62 to 1.14 for behavior support interventions. No reading intervention measured a behavior outcome, and no behavior support intervention measured a reading outcome. The two combined reading with behavior support interventions found positive effects on reading fluency (Tau-U range: 0.03 to 0.96), and only one of these studies measured behavior. Findings provide evidence for word reading instruction to improve word reading outcomes and self-monitoring and function-based interventions to be effective at improving student behavior. Future reading intervention research is needed to better understand how to best improve the reading and behavioral outcomes for SWRD+ADHD in grades K-12. A PRISMA-compliant abstract can be found at https://bit.ly/swrdadhd_osf.