This experimental study examined the effect of a differentiated, enriched reading program on students' oral reading fluency and comprehension using the schoolwide enrichment model-reading (SEM-R). Treatment and control conditions were randomly assigned to 63 teachers and 1,192 second through fifth grade students across five elementary schools. Using multilevel modeling, significant differences favoring the SEM-R were found in reading fluency in two schools (Cohen's "d" effect sizes of 0.33 and 0.10) and in reading comprehension in the high-poverty urban school (Cohen's "d" = 0.27), with no achievement differences in the remaining schools. These results demonstrate that an enrichment reading approach, with differentiated instruction and less whole group instruction, was as effective as or more effective than a traditional whole group basal approach. (Contains 13 tables.)