We examine the efficacy of an intervention to improve word reading and reading comprehension in fourth- and fifth-grade students with significant reading problems. Using a randomized control trial design, we compare the fourth- and fifth-grade reading outcomes of students with severe reading difficulties who were provided a researcher-developed treatment with reading outcomes of students in a business-as-usual (BAU) comparison condition. A total of 280 fourth- and fifth-grade students were randomly assigned within school in a 1:1 ratio to either the BAU comparison condition (n = 139) or the treatment condition (n = 141). Treatment students were provided small-group tutoring for 30 to 45 minutes for an average of 68 lessons (mean hours of instruction = 44.4, SD = 11.2). Treatment students performed statistically significantly higher than BAU students on a word reading measure (effect size [ES] = 0.58) and a measure of reading fluency (ES = 0.46). Though not statistically significant, effect sizes for students in the treatment condition were consistently higher than BAU students for decoding measures (ES = 0.06, 0.08), and mixed for comprehension (ES = -0.02, 0.14).