Trajectories of expressive language development are highly heterogeneous in autism. Yoder et al. found that parental responsiveness, child response to joint attention, child communicative intent and consonant inventory were unique predictors of expressive language growth in minimally verbal preschoolers 16 months later (n = 87). This study applied these predictors to an independent sample, over a 12-month period (n = 27). A broader measure of phonetic repertoire, combining reported, elicited and observed speech sounds, was included to further understand the contribution of speech production skills. Expressive language growth was highly variable: 65% remained minimally verbal at mean age 5;2, while 7% gained over 340 words. Contrary to expectations, communicative intent, parent responsiveness and response to joint attention were not found to predict expressive language growth or outcome. In contrast, both consonant inventory and phonetic repertoire were significant predictors (adjusted R[superscript 2] = 0.29 and 0.45). These results underscore the contribution of speech production abilities to expressive language development in this population, which may reflect an additional deficit rather than a consequence of core autism symptoms. Future work should include those with the most persistently limited expressive language, so that findings can be generalized and additional barriers to communication identified and addressed.