There is no debate that teaching students to read is an important goal of education. School districts have the challenging tasks of choosing an effective research-based reading program to implement and then ensuring that reading instruction results in improved reading achievement. The Spring Valley School District was faced with these challenges and the urgency to make changes. The biggest change was to implement a new reading program. The new reading program, "Bookworms: A Comprehensive K-5 Literacy Program," appeared to be a promising reading program, but more research was needed to claim that it is an effective and successful reading program. This mixed-methods research involved both qualitative and quantitative measures with two distinct purposes. The first purpose was to examine "Bookworms" and determine if the components and resources of the program provide evidence of a tiered approach to reading instruction. A narrative case study was used to identify evidence in "Bookworms" that supports the researched components of RTI, the foundational reading skills proposed by The National Reading Panel, and the shifts in instruction required to implement the Common Core State Standards. The second purpose was to determine if implementation of "Bookworms" had an effect on reading achievement and reading proficiency of elementary students in fourteen elementary schools in the Spring Valley School District. MAP and PARCC scores from the 2015-2016 school year, before the implementation of "Bookworms," were compared to MAP and PARCC data for the same groups, or cohorts, of students from the 2016-2017 school year, after one year of "Bookworms" implementation. Initially, a descriptive analysis was conducted; then, a "t"-test for dependent means was conducted for each cohort to see if there were statistically significant differences in the scores. The hypothesis for this study was that the implementation of "Bookworms" would result in a statistically significant improvement in reading achievement and reading proficiency of students in third, fourth, and fifth grades in the Spring Valley School District as measured by MAP and PARCC. The results of this mixed-methods research revealed that "Bookworms" provides a unique tiered approach to reading instruction with Tier 1 and Tier 2 reading components. There is substantial evidence to support RTI components, the NRP's recommendations for reading instruction, and the shifts in instruction from the CCSS. Additionally, the results of this research suggest that the implementation of "Bookworms" had a statistically significant effect on reading achievement scores on MAP and PARCC for each cohort of students studied. [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/en-US/products/dissertations/individuals.shtml.]