This article tests conflicting theories of schools as institutions by studying how the relationship between teacher credentials and student learning is moderated by school sector. I use large-scale institutional data on primary school students from the Indiana Department of Education and a multilevel model of student test score growth in mathematics. The model utilizes fixed effects at the student- and school-level, with the aim of identifying the causal effect of teachers and schools by leveraging students who move across school sectors.Consistent with previous research (Clotfelter, Ladd, and Vigdor 2007), I find no effect for teacher degree level or certification status, and this does not vary by sector. However, a teacher's years of experience is strongly related to growth and varies depending upon school sector. While charter school teachers tend to see lower test score growth in their students, this effect is lessened when comparing teachers in the initial stage of their career and in high-poverty schools, both of which are more common in Indiana's charter schools. On the other hand, I find that students placed with Catholic school teachers who are in the first six years of their career are expected to experience substantially less growth than students placed with traditional public school teachers within the first six years of their career. However, more experienced Catholic and traditional public school teachers are indistinguishable. These findings contradict current institutional models of schooling, and suggest that school sectors should be considered as distinct institutions with different isomorphic tendencies. I conclude by speculating about the classroom-level structural obstacles that teachers face, and suggest future opportunities for research into the mechanisms that mediate these findings.