Purpose: This study provides milestones for phonological development in African American English (AAE) speakers who are learning Mainstream American English (MAE) as a second dialect. Method: The Dialect Sensitive Language Test (DSLT; H. Seymour, T. Roeper, & J. G. de Villiers, 2000) was administered to a nationwide sample of typically developing children ages 4 through 12: 537 speakers of AAE as a first dialect and 317 speakers of MAE as a first dialect. DSLT items tested all consonant segments and many clusters of MAE in initial and final position. The age at which each dialect group reached 90% criterion for each segment in each position was compared. Results: Several phonetic elements that are contrastive between the dialects (i.e., differentiate the dialects) in word-"final" position were found to be similar in the 2 groups in word-"initial" position. Only /[eth]/ was contrastive in both positions. We confirm the later acquisition of certain phonological segments and structures by AAE speakers compared to MAE speakers and report their earlier mastery of other elements of MAE phonology. Conclusion: Both segmental and phonotactic development show different trajectories for AAE and MAE. Thus, initial diagnosis of impairment for AAE children should focus only on mastery of noncontrastive segments and structures that share a similar developmental profile for the 2 dialect groups.