This study contributes to the science of teaching reading by illustrating how a ubiquitous classroom practice -- read alouds -- can be enhanced by fostering teacher language practices that support students' ability to read for understanding. This experimental study examines whether and to what extent providing "structured teacher read aloud" supplements in a social studies read aloud can allow students to leverage a familiar science schema and thereby positively impact reading comprehension outcomes. Treatment students received a single social studies read-aloud on the story of Apollo 11 with structured teacher read aloud supplements while control students received the same read-aloud story but without structured supplements. Effect sizes from hierarchical linear models indicated that students in the treatment condition significantly outperformed students in the control condition on four measures of domain-specific reading comprehension. Further exploratory analyses using structural equation modeling examined the extent that teacher language mediated the treatment effect. Results indicated that teachers going above and beyond the intervention script explained 67 percent of the treatment effect. Structured supplements for read alouds can help students see important connections between schemas, which ultimately aids in reading comprehension.