Galactic-scale star formation depends both on the supply of gas and the efficiency at which that gas is converted into stars; both these factors vary with galactic mass. To study these processes together, galaxy simulations require a model for gas loss from stellar feedback and a star formation prescription tied to the molecular gas. In this talk, I will use cosmological simulations of dwarf and spiral galaxy formation with efficient supernova feedback and molecular hydrogen-based star formation to examine how star formation histories vary with halo mass. The resulting galaxies have rising rotation curves and realistic stellar masses and gas fractions. I will discuss how stellar feedback reduces the amount of low-angular momentum baryons to produce more realistic galaxies and how the efficiency of that gas loss is affected by the ISM model. I will also use paired simulations of dwarf and spiral galaxies with similar formation histories to show how a combination of lower mid-plane pressures and metallicities reduces the molecular gas and, therefore, the star formation efficiency in dwarf galaxies.