Special educators serving students with emotional/behavioral disorders (EBD) depend on their principals' support, yet prior research has not explored principals' roles in supporting these programs. Using constructivist grounded theory methods, we analyzed interviews with five U.S. elementary school principals about their roles in supporting self-contained programs for students with EBD. Principals held widely varying "conceptions of students with EBD," "visions" for their program, and understandings of their own "roles and responsibilities" for their programs; collectively, interactions among these gave rise to principals' "senses of agency," both for the program's capacity to be a causal agent in promoting student growth and their own capacity, as leaders, to improve the program. Our findings indicate the centrality of principals' conceptions of EBD for how they support self-contained programs for students with EBD, which has important implications for future research and practice regarding principal leadership for special education.