The primary purposes of the study are to investigate what teachers experience while using the Classroom Diagnostic Tools (CDT) and to relate those experiences to the rate of growth in students' mathematics achievement. The CDT contains three components: an online computer adaptive diagnostic test, interactive web-based student reports, and links to resources and materials in the Standards Aligned System (SAS). The goal of the CDT is to decrease gaps in academic achievement and promote individual student growth. Through this study, the researcher answered the following research questions: 1. Are there significant differences in growth rates in mathematics achievement between students who participate in classrooms that use the CDT and students in classrooms which do not use the CDT? 2. Are there significant differences in growth rates in mathematics achievement among classrooms that use the CDT? 3. Did the teachers have a positive, negative, or neutral experience with their use of the CDT? 4. Are there relationships between how the use of the CDT is experienced by teachers and the growth rates in mathematics achievement of the students? This research study used a quasi-experimental design with a pretest and posttest, which took place over a five-month period from September 2011 to January 2012. Qualitative interviews were conducted with the teachers during the study to gather information about their experiences using the CDT. Results of the quantitative data analysis showed the use of the interactive web-based student reports and links to the SAS did not produce a significant difference in growth rates when comparing the control group to the experimental groups. Further analysis of the achievement data also found significantly different growth rates among experimental groups. Analysis of qualitative data indicated that results in student achievement were related to what the teachers experienced with the use of the CDT. The groups which had a positive experience showed significant growth rates over time and the groups with neutral and negative experiences did not show significant growth over time. Key factors to significant growth rates included: providing training on effective use of the tool, use of student results and links to the SAS for planning instruction in the daily mathematics class, and one-on-one student conferencing to provide timely and specific feedback regarding the assessment results. [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.]