Public schools are examining their policies and instructional practices to address the achievement gap exposed by the reporting requirements of NCLB (Wenglinski, 2004). As accountability measures and stakes rise, there is a call for an improved use of scientific evidence to inform educational policymaking (Wiseman, 2010). In terms of the achievement gap, national studies at the secondary level show when students are grouped according to ability there is a rise in achievement inequality between the groups (Gamoran & Mare, 1989; Hoffer, 1992). The purpose of this study is to determine if there is a tangible, measurable academic benefit to homogeneously grouping high school honors English students in a diverse, suburban school district in Washington State. The following research question guided this study: To what extent, if any, does ability grouping of high achieving students defined as 9 th and 10th grade honors English students in a suburban Washington State school district, affect their performance on state and pre-college assessments of reading and writing achievement when controlling for student mutable variables? The research design used a non-experimental, explanatory associational design. Student achievement measures were examined before, during, and after high school students were placed in either like-ability (homogeneous) or mixed-ability (heterogeneous) groups when receiving honors English instruction in both their 9th and 10th grade years. The findings of this study indicate that type of grouping is not always a significant contributor to students' scores on state and pre-college assessments of reading and writing achievement. In models where grouping was a significant contributor, the favored grouping type was not homogeneous but heterogeneous grouping. Due to the relatively small sample size of this study, it is recommended that additional studies be done to answer the research question. This question is essential in our educational system's continued pursuit of equality of educational outputs; or in other words, closing and eliminating the achievement gap. It is recommended that a larger-scale experimental, quantitative study be done to determine if the results of this study can be replicated. [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.]