Today's grading practices mirror those of the early 1900s, and despite myriad research suggesting they are invalid, unreliable, and a hindrance to student learning, many teachers continue detrimental practices such as using 100-point percentage scales averaging all academic and nonacademic factors together into a single grade, and using grades to control student behavior. One grading reform effort gaining recent traction is standards-based grading (SBG), which involves grading students based on their proficiency against specific standards, removing behavioral influences from academic grades, and allowing multiple opportunities to demonstrate proficiency. Due to a stronghold of traditional grading beliefs and a lack of empirical research regarding the effectiveness of SBG practices on student learning, many educators are hesitant to adopt SBG practices. The purpose of this qualitative phenomenological study was to explore high school teachers' perceptions of the effects of SBG on planning, instruction, assessment, environment, and students' characteristics and behaviors. Seven high school teachers utilizing SBG practices participated in this study, and data were collected via semi-structured interviews, observations, and document review. Twelve themes emerged from data analysis: (1) Planning, instruction, and assessment become more purposeful, (2) Communication is clear, (3) Old habits die hard: Compromises are made between adopting recommended SBG practices and maintaining tradition, (4) SBG requires systemic change, (5) SBG creates an environment conducive to learning, (6) An SBG climate meets students' needs, (7) Teachers must find new ways to promote and enforce desirable behaviors, (8) Student conversations become more learning-focused, (9) Students shift toward growth mindset, (10) Students still "play the game" with grades, (11) Students' accountability initially decreases, and (12) In time, students take more ownership for their learning. Based on the findings of this study, the researcher concluded that SBG "makes sense" as a viable option for grading reform because it makes high school teachers' planning, instruction, assessment, and environment more purposeful, successful, and enjoyable, and teachers perceive increased growth mindset and ownership in students after an initial implementation dip. Findings led to several recommendations for administrators, teachers, students, and parents, including the need for systemic policies and practices that foster implementation consistency and promote desirable student work habits, professional development disseminated by knowledgeable teacher leaders embedded within professional learning communities, acknowledgment and addressing of teacher beliefs and reservations, teamwork committed to implementing one change at a time, and an overall focus on the potential long-term benefits of SBG to help withstand an initial implementation dip. [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.]