The purpose of this study was (1) to examine the causal effects of READ 180, a mixed-methods literacy intervention, on measures of word reading efficiency, reading comprehension and vocabulary, and oral reading fluency and (2) to examine whether print exposure among children in the experimental condition explained variance in posttest reading scores. A total of 294 children in Grades 4–6 were randomly assigned to READ 180 or a district after-school program. Both programs were implemented 4 days per week over 23 weeks. Children in the READ 180 intervention participated in three 20-min literacy activities, including (1) individualized computer-assisted reading instruction with videos, leveled text, and word study activities, (2) independent and modeled reading practice with leveled books, and (3) teacher-directed reading lessons tailored to the reading level of children in small groups. Children in the district after-school program participated in a 60-min program in which teachers were able to select from 16 different enrichment activities that were designed to improve student attendance. There was no significant difference between children in READ 180 and the district after-school program on norm-referenced measures of word reading efficiency, reading comprehension, and vocabulary. Although READ 180 had a positive impact on oral reading fluency and attendance, these effects were restricted to children in Grade 4. Print exposure, as measured by the number of words children read on the READ 180 computer lessons, explained 4% of the variance in vocabulary and 2% of the variance in word reading efficiency after all pretest reading scores were partialed out.