Purpose: The current study used an intervention design to test the hypothesis that parent input sentences with diverse lexical noun phrase (NP) subjects would accelerate growth in children's sentence diversity. Method: Child growth in third person sentence diversity was modeled from 21-30 months (n = 38) in conversational language samples obtained at 21, 24, 27, and 30 months. Treatment parents (n = 19) received instruction on strategies designed to increase lexical NP subjects (e.g., "The baby[underlined] is sleeping."). Instruction consisted of one group education session and two individual coaching sessions which took place when children were approximately 22-23 months of age. Results: Treatment substantially increased parents' lexical NP subject tokens and types (?[subscript p][superscript 2] = 0.45) compared to controls. Children's number of different words was a significant predictor of sentence diversity in the analyses of group treatment effects and individual input effects. Treatment condition was not a significant predictor of treatment effects on children's sentence diversity, but parents' lexical NP subject types was a significant predictor of children's sentence diversity growth, even after controlling for children's number of different words over time. Conclusions: These findings establish a link between subject diversity in parent input and children's early grammatical growth, and the feasibility of using relatively simple strategies to alter this specific grammatical property of parent language input.