Grades are ubiquitous in schools and have significant consequences in students' lives. Over a century of research has reported variability in teachers' grade compositions and grading practices. Although measurement experts have advocated for grades to represent student achievement alone, teachers continue to include nonachievement factors, such as growth, effort, and work completion, in their grading decisions. Grading experts have endorsed standards-based grading practices to strengthen the validity and meaning of teachers' grades, which requires teachers to report students' achievement and behaviors separately. Researchers have also encouraged additional studies of teachers' underlying beliefs and perceptions about grading to understand better why they make their decisions. This study employed a constructivist grounded theory methodology to explore teachers' grading practices and beliefs in three different school contexts using three different grading systems: traditional letter grading, a school-specific grading system that separated students' academic achievement and learning behaviors, and a hybrid of traditional and standards-based grading. Data included semistructured interviews with teachers and school and district administrators. Data analysis utilized constant comparative methods throughout initial and focused coding, memoing, and sorting to generate and strengthen theoretical development. This study proposes a theory about the factors influencing teachers' grading practices. More specifically, this study found that teachers' grading practices and beliefs were influenced by the grading system they used and their beliefs about students' ability and motivation. Teachers attributed their beliefs about students' ability and motivation to their perceptions about their parents and home lives, coded racially and socioeconomically. A combination of the grading system and beliefs about students informed teachers' grading purposes, which in turn, informed their grading practices. The findings from this study have implications for school and district grading policies, teachers' grading practices, and grading reform initiatives. [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://bibliotheek.ehb.be:2222/en-US/products/dissertations/individuals.shtml.]