"Xtreme Reading" is a supplemental literacy curriculum designed to improve the literacy skills of struggling students in grades 6 to 12. The curriculum is primarily designed to help students improve their vocabulary, decoding, fluency, and reading comprehension skills. To ensure a productive learning environment, students initially learn social skills associated with creating a supportive learning community, including how to participate in certain class activities (for example, whole-group discussion, small-group work, partner work, transitions). They also participate in a motivational program whereby they discuss their hopes and dreams for the future and set personal goals related to reading and other life areas. The "Xtreme Reading" program includes teacher-led whole-group instruction, cooperative group work, paired practice, and independent practice. This What Works Clearinghouse (WWC) intervention report, part of the WWC's Adolescent Literacy topic area, explores the effects of "Xtreme Reading" on student literacy achievement and comprehension (including reading comprehension and vocabulary skills). The WWC identified four studies of "Xtreme Reading," two of which meet WWC standards. The evidence presented in this report is from studies of the effects of "Xtreme Reading" on ninth-grade students--including 81% non-White and 19% White students-- from largely urban and diverse school districts. [For the Intervention Brief, see ED611356. For the Intervention Snapshot, see ED611358.]