Narration has been shown to be a foundational skill for literacy development in school-age children. Elementary teachers routinely conduct classroom lessons that focus on reading decoding and comprehension, but they rarely provide instruction in oral narration (Hall et al., 2021). This multisite randomized controlled trial was designed to rigorously evaluate the efficacy of the "Supporting Knowledge of Language and Literacy" ("SKILL") intervention program for improving oral narrative comprehension and production. Three hundred fifty-seven students who were at-risk for language and literacy difficulties in Grades 1-4 in 13 schools across seven school districts were randomly assigned to the "SKILL" treatment condition or a business as usual (BAU) control condition. "SKILL" was provided to small groups of two to four students in 36 thirty-minute lessons across a 3-month period. Multilevel modeling with students nested within teachers and teachers nested within schools revealed students who received the "SKILL" treatment significantly outperformed students in the BAU condition on measures of oral narrative comprehension and production immediately after treatment. Oral narrative production for the "SKILL" treatment group remained significantly more advanced at follow-up testing conducted 5 months after intervention ended. Improvements in oral narration generalized to a measure of written narration at posttest and the treatment advantage was maintained at follow-up. Grade level did not moderate effects for oral narration, but it did for reading comprehension, with a higher impact for students in grades 3 and 4. [For the corresponding grantee submission, see ED622886.]