This study investigated a Tier 2 intervention in the context of a response-to-intervention (RTI) model for 123 fourth-grade students identified as having a high probability of reading failure. A randomized control trial was used to evaluate the effects of a 24-session multicomponent supplemental intervention targeting fluency and expository comprehension of science texts. Intervention students performed significantly higher on science knowledge and comprehension strategy knowledge and use, but not on word reading, fluency, or other measures of reading comprehension. Moderators of intervention effects were also examined; children at higher risk in the intervention condition appeared to benefit more in comparison to lower probability children in intervention and compared to higher probability children in the control condition. (Contains 4 tables.)