Purpose: This study had 2 principal aims: (a) to examine whether children who spoke Nonmainstream American English (NMAE) frequently in school at the end of kindergarten increased their production of Mainstream American English (MAE) forms by the end of first grade, and (b) to examine concurrent and predictive relations between children's NMAE use and reading skills. Method: A longitudinal design was implemented with 49 children who varied in their spoken NMAE production in kindergarten. Word reading, phonological awareness, and receptive vocabulary skills were measured at both time points. Results: Analyses indicated that most children significantly increased their production of MAE forms between the 2 time points; however, this change was not associated with change in letter-word reading and phonological awareness skills. Regression analyses showed that NMAE use in kindergarten contributed significantly and independently to the variance in word reading in first grade, even after accounting for phonological awareness (although word reading in kindergarten was the best predictor of word reading in first grade). Conclusions: The findings extend previous reports of a significant relation between NMAE use and reading among young children. Theoretical, research, and educational implications of the findings are discussed. (Contains 3 tables and 1 figure.)