Scholars and reformers in the United States have called for converting large high schools into smaller units to provide a more effective, personal, and culturally responsive education for all students. Current literature argues that such "conversion high schools" should break into fully autonomous small schools rather than more interdependent smaller learning communities (SLCs). In contrast to existing recommendations, this comparative case study identifies four potential advantages of interdependent SLCs. A longitudinal study of teacher collaboration and teaching practices conducted over two years at two conversion high schools suggests that retaining a degree of interdependence among sub-units in conversion high schools may: support teaching and learning of specific academic subjects; promote more learning from other subunits on the campus of the high school; reduce the stress and chaos that accompany high school conversion; and offer more support for new teachers. (Contains 1 note, 1 table, and 1 figure.)