Reading performance among Grade 11 students has been low in the local school district under study. Schools within the boundaries of that setting have implemented research-based interventions to curb this problem of poor reading performance. A quasi-experimental, causal-comparative study was conducted to investigate the effect of Marzano's 6-step process to vocabulary development on students' performance in reading. The study was based upon Bruner's theory of spiral curriculum, which promotes teaching the same concepts at all grade levels at suitable levels of complexity. This study also followed the principles of Fisher, Frey, and Lapp regarding the implementation of program interventions. The major question guiding this study was whether Grade 11 students at the local high school who experienced 18 months of vocabulary intervention program made significant progress on their Grade 11 VITAL-S scores when compared to Grade 11 students in the same category who took the test 1 year earlier and experienced the intervention for 5 months. The standardized test scores of 2 groups of students from 2009 and 2010 school years were used as the data for analysis. A one-way ANOVA was conducted to compare students' test scores and to determine the effect of the intervention on reading scores. There was a statistical difference in the performances between groups. This finding indicated that the vocabulary program had a positive effect on students' reading performance. The project for this study, which has been presented as a white paper, is available to the school improvement team and district officials. The targeted school's program could serve as a model for the district and may solidify implementation strategies that positively impact the problem of poor reading performance at the school, district, and territorial levels. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com.bibliotheek.ehb.be/en-US/products/dissertations/individuals.shtml.]