Experts laud the potential of educational technology (edtech) to promote reading among students with disabilities, but supporting evidence is lacking. This study evaluated the effectiveness of the Lexia® Core5® Reading edtech program (Core5) on the Measures of Academic Progress® (MAP) Growth Reading™ and easyCBM oral reading fluency performance of students with reading or language-based disabilities in Grades K to 5. Core5 systematically addresses multiple reading domains and previously was effective in general education. We hypothesized treatment students using Core5 would outperform controls on the reading assessments. This was a cluster randomized effectiveness evaluation, with condition assignment by school (three treatment and two business-as-usual control schools). Participating students in Grades K to 5 (N = 115; nTreatment = 65) were flagged by their Chicago-area district as needing reading intervention and had Individualized Education Program (IEP) designations of specific learning disability, speech or language impairment, or developmental delay. Treatment students used Core5 to supplement Tier 1 instruction for an average of 58.76 minutes weekly for 24.58 weeks. Regressions revealed treatment students outperformed controls on MAP ([Beta] = 3.85, CI = 0.57-7.13, p = 0.022, d = 0.24), but there were no differences for oral reading fluency. MAP findings confirm edtech can effectively supplement reading instruction for this population.