This study examined phonological sensitivity in 238 children from middle- to upper-income families and 118 children from lower-income families across different levels of linguistic complexity. Children ranged in age from 2 to 5 years. Overall, the results indicated that as children increased in age, phonological sensitivity both increased in absolute terms and became more stable. Significant social class differences in growth of phonological sensitivity were also obtained. Phonological sensitivity at different levels of linguistic complexity (e.g., syllables, phonemes) was substantially interrelated at each age and predicted word reading ability in older children independently of language skills and letter knowledge. These results indicate that phonological sensitivity can be assessed in young preschool children and that lower levels of phonological sensitivity may serve as developmental precursors to higher levels of phonological sensitivity. The development of phonological processing is an important precursor to the acquisition of early reading skills (e.g., Adams, 1990; Wagner & Torgesen, 1987). Phonological processing refers to the use of phonological information (i.e., the sounds of one's language) in processing written and oral language. A growing body of research indicates that individual differences in one form of phonological processing, phonological sensitivity, are causally related to the normal acquisition of beginning reading (e.g., Bryant, MacLean, Bradley, & Crossland, 1990; Wagner & Torgesen, 1987; Wagner, Torgesen, & Rashotte, 1994). Children who are better at detecting and manipulating syllables, rhymes, or phonemes are quicker to learn to read, and this relation is present even after variability in reading skill due to factors such as IQ, receptive vocabulary, memory skills, and social class is partialed out (Bryant et al., 1990; Wagner & Torgesen, 1987; Wagner et al., 1994). The majority of evidence linking phonological sensitivity in prereaders with the development of reading has come from studies that have assessed children's phonological sensitivity at the point of school entry but prior to formal reading instruction. For example, Share, Jorm, MacLean, and Mathews (1984) found that children's phonological sensitivity, measured at the beginning of kindergarten with a phoneme segmentation task, was the single best predictor of