The study reviewed in this paper examined the effects of a web-based tutoring program, "Intelligent Tutoring of the Structure Strategy" ("ITSS"), on the reading comprehension of fourth-grade students in language arts classrooms. The analysis included 1,875 to 2,371 fourth-grade students from 100 to 117 classrooms in Pennsylvania elementary schools (sample sizes varied across outcome measures). Schools volunteered to participate in the study. Within each school or group of similar schools, researchers randomly assigned 131 classrooms to either participate in "ITSS" or serve as the comparison group, which followed the regular school curriculum for language arts. Students in the "ITSS" classrooms used the system for one class period a week for 6-7 months as a partial substitute for their regular language arts curriculum (i.e., time spent using "ITSS" replaced regular instructional time). This study assessed the effectiveness of "ITSS" immediately after the end of the intervention by comparing the reading comprehension of students in the "ITSS" classrooms with students in the comparison class-rooms. Reading comprehension was measured with a standardized test (the Gray Silent Reading Test, or GSRT) and five researcher-designed measures on two types of text structures: comparison type texts and problem/solution type texts. The study authors reported, and the WWC confirmed, that "ITSS" had a statistically significant positive effect on the reading comprehension of fourth-grade students as measured by the researcher-designed tests. The study authors also reported, and the WWC confirmed, no statistically significant effects of the intervention on the GSRT. The research described in this report meets WWC evidence standards without reservations. The study is a well-implemented randomized controlled trial. [The following study is the focus of this "Single Study Review:" Wijekumar, K. K., Meyer, B. J. F., & Lei, P. (2012). "Large-scale randomized controlled trial with 4th graders using intelligent tutoring of the structure strategy to improve nonfiction reading comprehension." "Educational Technology Research and Development," 60(6), 987-1013.] The following are appended: (1) Study details; (2) Outcome measures for the reading comprehension domain; and (3) Study findings for the reading comprehension domain. A glossary of terms is included. (Contains 2 endnotes.)