This synthesis extends a report of research on extensive interventions in kindergarten through third grade (Wanzek & Vaughn, 2007) to students in Grades 4 through 12, recognizing that many of the same questions about the effectiveness of reading interventions with younger students are important to address with older students, including (a) how effective are extensive interventions in improving reading outcomes for older students with reading difficulties or disabilities and (b) what features of extensive interventions (e.g., group size, duration, grade level) are associated with improved outcomes. Nineteen studies were synthesized. Ten studies met criteria for a meta-analysis, reporting on 22 distinct treatment/comparison differences. Mean effect sizes ranged from 0.10 to 0.16 for comprehension, word reading, word reading fluency, reading fluency, and spelling outcomes. No significant differences in student outcomes were noted among studies related to instructional group size, relative number of hours of intervention, or grade level of intervention. (Contains 4 tables.)