Purpose: We sought to confirm predictions based on past findings that pretreatment mean length of utterance (MLU) would predict which of 2 grammatical treatments would best facilitate generalized and maintained grammatical development in preschoolers with specific language impairment (SLI). Method: The participants were 57 preschoolers with SLI. A randomized group experiment was used. The 2 grammatical treatments were broad target recasts (BTR) and milieu language teaching (MLT). MLU was assessed at Time 1 in 2 conversational language samples. Growth rate of productive grammar was quantified using growth curve modeling on the Index of Productive Syntax (IPSyn) from 2 conversational language samples at each of 6 measurement periods. Results: Predictions were confirmed for children with initially low MLU but not for children with initially high MLUs. MLT facilitated growth of grammar better than BTR in children who were initially in Brown's stage I. Effects maintained 5 months after treatment ended.