Purpose: We evaluated whether children whose inaccurate /[voiced alveolar approximant]/ productions showed evidence phonetic differentiation with /w/ at 3.5-4.5 years of age improved in /[voiced alveolar approximant]/ production over the next year more than children whose inaccurate productions did not show evidence of such differentiation. We also examined whether speech perception, inhibitory control, and vocabulary size predicted growth in /[voiced alveolar approximant]/. Method: A set of typically developing, monolingual English-speaking preschool children (n = 136) produced tokens of /[voiced alveolar approximant]/- and /w/-initial words at two time points (TPs), at which they were 39-52 and 51-65 months old. Children's productions of /[voiced alveolar approximant]/ and /w/ were narrowly phonetically transcribed. Children's productions at the earlier time point were rated by naïve listeners using a visual analog scale measure of phoneme goodness; these ratings were used to assess the degree of phonetic differentiation between /[voiced alveolar approximant]/ and /w/. Results: Accuracy for both phonemes varied considerably at both TPs. The growth in accuracy of /[voiced alveolar approximant]/ between the two TPs was not predicted by any individual-differences measures, nor by the degree of differentiation between /[voiced alveolar approximant]/ and /w/at the earlier time point. Conclusion: Low vocabulary size, low inhibitory control, poor speech perception, and the absence of early phonetic differentiation are not necessarily limiting factors in predicting /[voiced alveolar approximant]/ growth in individual children in the age range we studied.