Prisons across the United States of America are faced with finding ways to reduce illiteracy rates across adult education. One strategy is to offer reading programs that are based on the science of reading. Thus, the purpose of this study was to determine if adults in treatment groups across five midwestern correctional institutions who received a modification of Orton-Gillingham (i.e., Pure and Complete Phonics, Nash, 2013) would outperform the control groups who received the institution's standard reading program. The student participants had fifth grade or lower scores on the Test of Adult Basic Education, and instruction was implemented for 15 weeks, 5 days a week for one hour a day by certified teachers. Pre-and post-data was collected using the Woodcock-Johnson Tests of Achievement III, and results indicated that students' reading performance on all reading measures exceeded that of the control group.