The purpose of this investigation was to examine the efficacy of a new preschool oral language and early literacy curriculum package ("Teaching Early Literacy and Language" ["TELL"]) for children with developmental speech and/or language impairment (DSLI) either as a primary (e.g., specific to speech and/or language) or secondary impairment (e.g., developmental delay that includes DSLI). Participants included 118 children (30 females, 88 males, M age = 53.58 months) with DSLI and their 29 preschool teachers. The design was a randomized controlled trial (RCT) with assignment to experimental versus contrast conditions at the classroom level. Teachers in "TELL" classes received formal training, in-class support, and mentoring to implement the curriculum. Dependent measures for the children included scores on the "Clinical Evaluation of Language Fundamentals-Preschool 2nd" edition (CELF-P2), the "Phonological Awareness Literacy Screening for Preschool" ("PALS-PreK"), the "Renfrew Bus Story" ("BUS"), and a receptive and expressive vocabulary measure developed for this investigation (VOCAB). Results indicated that when compared to the contrast group, children in the "TELL" condition demonstrated greater gains on the phonological awareness subtest of the "CELF-P2," the sentence length score of the BUS, the letter sounds, beginning sound awareness, and rhyme awareness subtests of the "PALS-PreK", and "VOCAB." Results suggest that the "TELL" curriculum package has promise for promoting gains in early literacy and oral language skills in preschool children with DLSI.