The present study used individual growth modeling to examine the role of specific forms (i.e., receptive, expressive, and definitional vocabulary and grammatical skill) and levels of oral vocabulary skill (i.e., 25th, 50th, or 75th percentile) in phonological awareness growth during the preschool and kindergarten years. Sixty-one, typically-developing, 3-, 4-, and 5-year-olds, all from middle- to upper-income families, participated in the year-long study. A comprehensive battery of standardized and unstandardized measures was used to assess phonological awareness, oral vocabulary (i.e., receptive, expressive, and definitional) and grammatical skill at baseline, and at 3, 6, and 9 months later. Receptive vocabulary was the strongest predictor of growth in phonological awareness for the sample as a whole, followed by expressive vocabulary and grammatical skill, respectively. In the full model, definitional level vocabulary did not make a significant contribution to growth in phonological awareness. Receptive vocabulary accounted for additional phonological awareness growth in the 3-year-olds, but not in 4- and 5-year-olds, while expressive vocabulary accounted for additional phonological awareness growth in 4- and 5-year-olds, but not in 3-year-olds. Post hoc analyses were conducted to explore the change in relations between phonological awareness and receptive and expressive vocabulary that was identified by the individual growth models. The post hoc results suggested that higher levels of expressive vocabulary (i.e., higher scores on the measures) are likely required to complete phonological awareness tasks with the most difficult operations and highest task demands, even if the linguistic unit involved is large. The theory of lexical reorganization attributes the origin and protracted development of phonological awareness to increases in vocabulary size (Metsala & Walley, 1998). The present study's results suggest that increases in vocabulary size might be necessary, but not sufficient, as a foundation for phonological awareness development. Expressive level vocabulary might also be needed to hold words in memory to perform complex manipulations required in higher-level phonological awareness tasks. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com/en-US/products/dissertations/individuals.shtml.]