Poor reading comprehension is a concern for all schools. The structure strategy has improved reading comprehension consistently for over 35 years. A web-based intelligent tutoring system to deliver the structure strategy (ITSS) was created to support wider dissemination of this powerful approach. This paper presents the findings from a large scale randomized controlled trial (129 classrooms) on the effects of ITSS on the reading comprehension of 4th grade rural and suburban students as measured by a standardized test as well as researcher designed measures. The design involved within school random assignment of ITSS to classrooms, and data analyses used hierarchical linear modeling. Both measures showed that the ITSS classrooms statistically significantly outperformed their control classroom counterparts on post-test measures.