Partitioning phase transformations in the solid state are principally subjected to two processes that take place: the redistribution, through long-range diffusion, of the partitioning element, and the lattice transformation taking place at the interface. Consequently, the usual approximation to consider one of these two processes as controlling the rate of the phase transformation is of limited accuracy. For a more accurate description, the so-called mixed-mode character of partitioning phase transformations is to be taken into account. In the present study, it is shown that the mixed-mode character can be quantified and that it has a significant effect on the kinetics. By means of examples involving either substitutional (Mo in Ti) or interstitial (C in Fe) partitioning elements, it is shown that a gradual change of the character of the transformation occurs during the phase transformation, shifting from initially interface-controlled (which implies the largest interface velocity) towards more diffusion-controlled.