Findings from previous cross-sectional studies showed that while toddlers around their first birthday imitate selectively, that is, they systematically omit some kinds of target action steps or they copy only the goal, but not the means of the modeled actions, older toddlers imitate more exactly. The aim of the present article is to provide longitudinal evidence for this developmental trend and to investigate how imitation of different kinds of target action steps contributes to inter-individual differences in overall imitation performance. The present analysis of longitudinal deferred imitation data contrasted toddlers' imitation of functional and relevant (FURE) versus arbitrary and irrelevant (ARIR) target action steps at the ages of 18 and 24 months. The results show that the difference between the imitation rates of these two kinds of target action steps decreased with age, supporting the developmental trend from selective towards more exact imitation. In addition, findings of the present analyses point to the prominent role of toddlers' imitation of arbitrary and irrelevant target action steps in shaping inter-individual variability of overall deferred imitation performance.