Two experiments on the development of subvocal rehearsal in short-term memory (STM) are reported in this study. According to the articulatory loop model of adult performance, rehearsing the names of visually presented stimuli involves extra mental operations compared with rehearsing items that are heard. We used this analysis to predict that rehearsal will appear later in the development of STM for pictured objects than for spoken words. To provide an indication of rehearsal, we manipulated the word length of these two types of stimuli. Experiment 1 tested children's ability to recall sequences of fixed length, while Expt 2 used a memory span procedure. The results supported our prediction in that STM for spoken words was sensitive to word length at all ages from 4 years upwards, while STM for pictured objects showed equivalent effects only in children aged over 8 years. Subsidiary analysis of the relation between recall of spoken words and speech rate confirmed previous evidence that the capacity of the articulatory loop remains approximately constant during development. We conclude that this rehearsal system is present from an early age, and that development involves a broadening of the range of stimuli which can gain access to it.