Scoring rubrics are widely employed across content areas and grade levels, including in high school biology classes. Besides regular external use within accountability systems, educators also have advanced their instructional use inside classrooms. In recent years, a consensus appears to be emerging in the educational literature that instructional use of rubrics is beneficial for student learning, and numerous examples in the research and practitioner literature establish their importance in teachers' planning, instruction, and assessment. We examine this assumption through close analysis of students' use of a scoring rubric in a high school biology classroom. We explore how instructional use of a scoring rubric influences biology teaching and learning activities, what messages about knowledge and learning such use conveys to students, and what influence such use may have on students' emergent understandings of what constitutes quality in biological thinking and practice. Our analysis suggests that instructional use of scoring rubrics can actually undermine the very learning it is intended to support. We discuss an alternative way to help students understand what constitutes high-quality work, and we draw implications for science teacher education.