This study examined the effectiveness of the intensive implementation of a multicomponent reading intervention ("Voyager Passport") with 306 fourth-grade students with severe reading difficulties. Students with reading comprehension achievement below the 15th percentile in the fall of fourth grade were randomly assigned to the intensive intervention or to typical school services. Students assigned to the intensive intervention were placed in instructional groups of two to three students and received daily, 45-minute sessions of supplemental, multicomponent reading intervention throughout the school year. Students in the intensive intervention significantly outperformed their peers receiving typical school services in word reading (effect size [ES] = 0.25) and word-reading fluency (ES = 0.19). Study groups performed similarly on measures of reading fluency and comprehension. Ultimately, students with severe reading difficulties accelerated their word reading and word-reading efficiency achievement, but the acceleration was not enough to also accelerate their reading fluency or reading comprehension. [For the corresponding grantee submission, see ED616060.]