This study describes the development of the Students' Conceptions of Mathematics as Sensible (SCOMAS) Framework and its application to the study of the conceptions of mathematics as sensible of students in a secondary mathematics classroom. The SCOMAS Framework begins with indicators that students conceive of mathematics as sensible and provides a categorization of these indicators into five types of student activity. Utilizing indicators and categories of activity the SCOMAS Framework provides a tool for documenting students' conceptions of mathematics as sensible. This study begins with a description of the methods used to develop an initial framework of indicators from the research literature. It then describes how the initial framework was used to investigate the conceptions of mathematics in a 9th grade algebra classroom. The study reports on the use of the initial framework as a tool to describe the dimensions of students' conceptions of mathematics as sensible and the changes in those conceptions over the course of an academic year. Finally, the study reports on how analysis of the classroom data helped shape the initial framework into the final SCOMAS Framework. [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.]