Purpose: In U.S. public schools, principals must implement reforms that require instructional leadership across subjects, though little is known about subject-specific supervision. Methods: Through interviews with 26 K-8 principals, we examine instructional leadership for science. Findings: Our findings showed that science supervision occurred rarely; principals used a "content-neutral" approach that did not emphasize science-specific aspects of instruction. Principals explained this in terms of external accountability pressures in literacy and mathematics, as well as their own lack of science knowledge. Implications: We argue for subject-specific resources for principal supervision. For classrooms to change, principals must provide subject-specific support for teachers.