The morphology of poly(ether-ester) multiblock copolymers with hard segments containing poly(tetramethylene isophthalate) is characterized as a function of the undercooling and hard-segment concentration in isothermal crystallization experiments. At fixed undercooling, the SAXS long spacing increases with decreasing hard-segment concentration and increases strongly with decreased undercooling. Room-temperature storage following crystallization is characterized by a T-c-dependent contraction of the long spacing. Similar effects are seen in variable-temperature SAXS thermal contraction experiments, where the decrease in the long spacing on cooling is more rapid at higher T-c for samples of comparable crystallinity. DSC results, and experiments with copolymers containing a mixture of isomers in the hard segments, suggest that both behaviors can be attributed to secondary crystallization on cooling. The observed contraction behavior is qualitatively consistent with models incorporating some form of "morphology control", where the noncrystalline layer thickness is viewed as a contributing factor governing crystallization on cooling. Crystallization of the copolymers is viewed as an extension of the homopolymer crystallization, with additional accounting for fractionation effects and the need to accommodate the soft segment within the semicrystalline microstructure.