Units of change in developmental velocity during a specified time interval. After having subtracted the mean velocity value at a previous age from that at a subsequent adjacent age to give one for ‘speed’ of development, then the resulting scores are again subtracted from each other (double differentiation) to give a measure of acceleration (the unit of change) between the two ages. Developmental acceleration obtained in this way can be used to indicate sudden changes (i.e., transitions) in a process of continuous development.
See Adolescent growth spurt, Developmental function, Developmental trajectories, Developmental velocity, Mid-growth spurt, Transition