Although "Corrective Reading Decoding" has been validated as effective over a wide range of students, there is a lack of information on its effectiveness with older students having intellectual and developmental disabilities (IDD). Thus, the purpose of this investigation was to determine the effectiveness of "Corrective Reading Decoding B1" on the reading skills of a high school student with IDD. Pre- and posttest data were collected on the "Woodcock-Johnson III (WJ-III)." Scores were compared to a previous administration of the "Woodcock-Johnson Revised (WJ-R)." Within-program assessments were also completed. Results showed that improvements occurred across the majority of the subtests and all reading clusters; gains were also evident when scores were compared to the normative group. Results of the within-program assessments showed mastery of skills taught within the "Corrective Reading Decoding B1" program. (Contains 1 table.)