This study investigates the effects and feasibility of an intervention for first-grade students at risk for reading difficulties or disabilities (RD). The intervention was provided by general education classroom teachers and consisted of 15 min whole-class comprehension lessons (Tier 1) and 30 min Tier 2 intervention sessions in word reading, comprehension, and text reading. First-grade teachers (n = 21), with 4-5 students at risk for reading difficulties and potential reading disability were randomly assigned to treatment or typical practice comparison conditions. Significant group differences were detected on all measures of word reading, decoding, and fluency. Effect sizes were educationally important for all measures of word reading, decoding, and reading comprehension; however, effects on standardized measures were smaller than those in prior studies with similar students in which intervention was typically provided outside the regular classroom. An exploratory analysis indicated that students at different parts of the pretest and posttest distributions responded more and less positively to the intervention, providing insights that may help guide future revisions. The study provides preliminary evidence of the intervention's promise for positively impacting student outcomes.