Reading fluency has been identified as a key component in effective literacy instruction (National Reading Panel, 2000). Instruction in reading fluency has been shown to lead to improvements in reading achievement. Reading fluency instruction is most commonly associated with guided repeated oral reading instruction. In the present retrospective study we examine the effects of a computer-based silent reading fluency instructional system called Reading Plus (Taylor Associates, Winooski, Vermont, USA) on the reading comprehension and overall reading achievement of a large corpus of students in an urban school setting. Findings indicate that the program resulted in positive, substantial, and significant improvements in reading comprehension and overall reading achievement on a criterion referenced reading test for Grades 5, 6, 7, 8, and 9 and on a norm-referenced test of reading achievement for Grades 4, 5, 6, 7, 8 and 10. Moreover, mean gains made by students in the Reading Plus intervention were greater than mean gains for all students at the state and district level. The findings were generally positive for all subpopulations studied, including special education and regular education students. Qualitative reports from teachers who participated in the study were also supportive of the program. Implications for the study are explored for particular subgroups of students and for the role of fluency instruction with struggling adolescent readers.