We examined data from an 18-week kindergarten vocabulary intervention study to determine whether treatment outcomes had differential effects that favored English language learners (ELLs) or English-only learners (EOLs) and whether the relationship between initial English general receptive vocabulary knowledge and response to vocabulary intervention differed as a function of language status. Participants from 3 northeastern U.S. elementary schools within 3 separate school districts were assigned to either a treatment condition (ELLs, n = 31; EOLs, n = 49) or no-treatment condition (ELLs, n = 17; EOLs, n = 25). Trained interventionists delivered direct vocabulary instruction using 1 storybook twice per week in 20- to 25-min sessions. Results from 2 × 2 analyses of variance indicated that participants performed better if they were (a) in the treatment condition rather than the no-treatment condition and (b) categorized as an EOL rather than an ELL with evidence of an interaction effect on a target-word knowledge measure (TWKM). Regression analyses indicated that (a) the centered pretest Peabody Picture Vocabulary Test-III (PPVT-III) accounted for a statistically significant proportion of the variance in posttest measures for treatment participants and (b) language status did not explain any additional variance in posttest measures. Each of the 3 mediation models for the dependent measures TWKM, PPVT-III, and listening comprehension, using the independent variable language status and the mediating variable centered pretest PPVT-III, resulted in full mediation. Findings indicate that treatment ELLs and treatment EOLs would most likely perform equally well on posttest target-word and general receptive vocabulary measures if they had similar initial English general receptive vocabulary knowledge.