Collaborative Strategic Reading (CSR) is a multicomponent reading intervention aimed at improving students' text comprehension. Two 1-year randomized controlled trials were conducted to determine the efficacy of CSR with seventh and eighth grade students. The Year 2 replication study was identical to the original Year 1 study except that the student sample was different and the teachers were more experienced in the Year 2 study since the same teachers taught during both years of the study. The primary research question for the replication study was to determine the efficacy of CSR on middle school students' reading comprehension when taught by relatively experienced teachers (year 2), and to contrast the impacts to those obtained when similar middle school students were taught by inexperienced CSR teachers (year 1). This study incorporated fidelity into multilevel analyses in order to more fully explore and document the relationship between implementation of CSR strategies by experienced teachers and middle school students' reading comprehension. This study was conducted in 6 middle schools in 3 school districts (two near urban and one urban) in Texas and Colorado that reflected a diverse student population who were provided daily English/language arts/reading instruction. Twelve teachers and 48 classes (treatment = 26, control = 22) participated during Year 2. Students in this study were two separate cohorts of seventh and eighth graders enrolled in English/language arts/reading classes. Researchers conducted a randomized control trial at two sites for both studies. The same set of pretest and posttest measures were administered prior to treatment and immediately following treatment for both. The reading achievement battery included the TOWRE, the Test of Silent Reading Efficiency and Comprehension (TOSREC), Test of Sentence Reading Efficiency (TOSRE), AIMSweb Maze passages for 7th and 8th Grades, and the Gates-MacGinitie Reading Test. Researchers also collected data on student characteristics (e.g., language and special education status, age, gender, ethnicity, reading proficiency) to examine comparability of groups. For quantitative analyses, multilevel modeling in Mplus 5.1 was used to estimate the effects of treatment and the moderating influence of important covariates. For fidelity analysis in Year 2, confirmatory factor analysis with categorical indicators was used to estimate factors related to fidelity and spillover, and the mediating effect of implementation was evaluated. The Year 2 trial results suggest that implementation was high in the treatment conditions and relatively low in the comparisons. Findings also indicate that implementation was consistent across program elements; treatment conditions had high implementation of all program elements, on average. These findings represent a model for replicating effective intervention in the context of evaluating the relative contribution of its respective components.