The education of students with disabilities (SWD) has undergone some significant changes within the public education system since the enactment of the Individuals with Disabilities Act (IDEA) and the No Child Left Behind Act (NCLB). Special education legislation has historically focused on equal access for all students. Too much time has been spent on educational access and not on student outcomes. Recently, the IDEA coupled with the NCLB has focused national attention on improving academic achievement of every child across the nation. The pairing of IDEA and NCLB raises the expectations of all students, including those SWD. In order to capitalize on student achievement, greater attention must be paid to the improvement of classroom assessment. Formative assessment may be at the heart of changing student achievement and motivation as well as teachers' expectations of these students. When teachers utilize formative assessment effectively, all students learn better (Black & Wiliam, 1998a; Popham 2006; Stiggins, 2002). The purpose of this study was to investigate teacher's perceptions about the influence of formative assessment on fourth grade SWD reading gains and the students' actual gains in the skills of: letter/sound recognition and word identification, reading comprehension and overall reading composite. Four special education teachers from two elementary schools located in a large middle-class school district in Suffolk County, Long Island were invited to participate in this study. The teachers in the study taught in either the integrated co-teaching or special class setting. Each integrated co-teaching classroom had no more than twelve special education students and no more than a total class size of 26. The special class did not have more than 15 special education students. The students with disabilities scores that were utilized in this study were all in the fourth grade and had been classified with a through the Committee on Special Education. The data for this study were collected using semi-structured interviews during which the participants were asked open-ended questions. Additionally, data were collected from the results of the Kaufman Educational Achievement Test, specifically the reading subtests of letter/sound identification, word recognition and reading comprehension. A mixed methodology was used in this study. An analysis of the themes, patterns, and discrepancies noted from the interview protocol was triangulated with data generated from the pre and post test information from the Kaufman Educational Achievement Test. Results indicated that when both the qualitative and the quantitative data were triangulated the teachers' perceptions and the actual student gains in reading were closely associated. The teachers' perceptions of their students' achievement were positive when they used formative assessments to guide their students learning in reading. The teachers believed that most or all of their students would be positively impacted by the use of the information gained from these assessments. The actual gains supported this to be true as the data showed that in most cases, all or most of the students demonstrated gains in their reading in at least one of the areas assessed. [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.]