Literacy is one of the most important skills needed for academic success. High school educators address the learning shortfall in reading through interventions. This mixed methods study evaluated the effectiveness of the "Read 180" intervention program on increasing the reading achievement of 9th and 10th grade general education students one to two grade levels below proficiency. Constructivism served as a theoretical framework for this study. "Ex post facto" quantitative data were gathered on 234 students who participated in the program for one semester and students who participated for one school year. Qualitative data were gathered from five "Read 180" teachers via semi-structured interviews. Analysis of quantitative data revealed significantly greater than expected annual Lexile score gains for 9th and 10th grade students who participated for one school year. Further analysis revealed 45% of participants in grade 9 and 43% of students in grade 10 who were in the "Read 180" program for one school year reached grade-level proficiency at the 50th percentile. Student participants for one semester had less growth, with average total Lexile score gains of 18.59L for students in grade 9 and 22.14L for students in grade 10. Analysis of qualitative data revealed themes, supporting the "Read 180" program as an effective intervention tool to raise student's reading achievement, instill confidence in struggling readers, and create an environment conducive to increasing their academic skills. This study contributes to the literature supporting the effectiveness of the "Read 180" program at the high school level. Further implications suggest that the "Read 180" program should be implemented for one full school year, schools should be selective in the students who are chosen to participate in the intervention, and a smaller class size is essential to the success of the program. This study illustrates the "Read 180" program can be an effective tool to increase the reading achievement of struggling readers within the general education setting. [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://bibliotheek.ehb.be:2222/en-US/products/dissertations/individuals.shtml.]