We examine the effects of a read aloud replication intervention designed to improve the vocabulary, comprehension, and expository and narrative language outcomes of first grade students. Thirty-nine first-grade classrooms from 12 schools were randomly assigned to a treatment (n=19) or comparison condition (n=20). Teachers in the treatment condition implemented a 19-week set of read aloud lessons during whole-class read aloud time. Read alouds included the systematic use of narrative and expository texts, before-, during-, and after-reading components, the use of teacher-facilitated text-based discourse, and explicit comprehension instruction. Results indicated main effects of treatment on vocabulary knowledge. Exploratory findings indicated a significant interaction effect of treatment and recommended features of read aloud instruction on all outcomes. Specifically, students of teachers in the treatment condition who were rated higher on adhering to recommended features of read aloud instruction had better outcomes on vocabulary, comprehension, and language outcomes on expository and narrative text than treatment teachers who closely followed intervention materials without dynamically adjusting to student responses. We discuss these findings in the context of other read aloud studies, including a previous study that used the same intervention in a different setting and with a less diverse sample of students.