Low reading skills constitute a serious achievement problem. Although there are remedial support in schools, between 2% and 6% of the student population continues to show persistent reading difficulties despite intensive intervention. The research problem in this study addressed the lack of effective reading interventions for students who were in Tier III of the Response to Intervention (RtI) process. Piaget's cognitive development theory, constructivism, and Vygotsky's zone of proximal development theory made up the theoretical framework. The purpose of this quantitative study was to determine the effects of "Fountas and Pinnell's Leveled Literacy Intervention (LLI)" on reading achievement of students in Grades 2-5. Reading achievement was measured using "Fountas and Pinnell's Benchmark Assessment System (BAS)" and "Measures of Academic Progress (MAP)" assessments. A quasi-experimental design was utilized to compare pre-and post- intervention data for students in Grades 2-5 who did or did not receive LLI instruction and were in Tier III of the RtI process. The sampling size was determined by the number of students who scored below the grade level expectation on the Fall 2015 BAS and MAP assessments. The experimental group consisted of 72 students and the control group consisted of 64 students. Data were collected and analyzed using ANCOVA. The pretest was treated as a covariate. The results of this study showed reading achievement scores were significantly higher for the experimental group on both posttests. This study contributed to positive social change by improving the welfare of students by increasing their reading achievement. [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.]