This quasi-experimental study was designed to test the impacts of a curriculum supplement, "Let's Know!", on the quantity and quality of language-focused comprehension instruction in pre-kindergarten to third grade classrooms. Sixty classrooms (12 per each of pre-K to grade 3) were enrolled in the study, with 40 teachers assigned to implement one of two versions of the experimental "Let's Know!" curriculum and 20 assigned to a control condition, in which they maintained their typical language-arts curriculum. Classroom observations, 90 min in duration, were collected near the end of the first unit's completion, about 4 to 5 weeks into the academic year. These observations were coded to examine impacts of "Let's Know!" instruction on two outcomes: (a) teachers' use of 18 language-focused comprehension supports and (b) general classroom quality. Study results using quantile regression showed that "Let's Know!" teachers used a significantly higher number of language-focused comprehension supports during "Let's Know!" instruction compared to the control teachers during language-arts instruction; the same finding was also true for general classroom quality. Quantile regression results showed the greatest differentiation in instructional quality, when comparing experimental and control teachers, for teachers in the middle of the distribution of general classroom quality. Study findings highlight the value of language-focused curricula for heightening comprehension-specific supports in pre-K to grade 3 settings. [This paper was prepared by a Task Force of the Language and Reading Research Consortium (LARRC) consisting of Laura M. Justice, Amy Pratt, Jessica Logan, and Shelley Gray.]