The purpose of this study was to investigate the response of kindergarten students at-risk for reading failure to a two-tiered vocabulary intervention delivered in the context of a shared storybook reading activity employing rich and robust vocabulary instruction. Rich vocabulary instruction is defined as explicit vocabulary instruction in which children are exposed to definitional and contextual explanations of word meanings in multiple contexts over multiple exposures and have the opportunity to process word meanings deeply. Previous research suggests that high and low achieving students benefit from rich, explicit vocabulary instruction. This stands in stark contrast to other research evidence suggesting that high and low achieving students have differential learning rates when taught with other types of vocabulary instruction, namely that at-risk, low achieving students do not learn as much as high achieving students when exposed to, for example, incidental vocabulary instruction. Furthermore, the emerging response to intervention model of instruction provides an instructional context in which rich vocabulary instruction may be delivered in successively intensive tiers for at-risk students for whom classwide, general instruction typically is not as effective as it is for their not at-risk peers. Participants included 92 kindergarten students from an elementary school in Central Virginia that serves a diverse group of children. All children received a general Tier 1 vocabulary intervention delivered with rich and robust vocabulary instructional methods. Twenty-four students identified as at-risk for reading failure based on low initial vocabulary scores as assessed by the PPVT-4 received an additional second tier of rich vocabulary instruction. Using a regression discontinuity experimental design, this study examined several issues related to rich vocabulary instruction including the relative benefit of Tier 2 instruction in addition to Tier 1 instruction, the effectiveness of different instructional methods within Tier 2, and learning gains and maintenance of vocabulary learning over time across both the comparison and treatment groups. Some results provided clear research evidence regarding the overall benefit of rich instruction; for example, after adjusting for initial vocabulary scores, both groups of students (at-risk and not at-risk comparison) demonstrated similar rates of learning in response to rich instruction and maintained learning over time. Other results, including those related to the relative benefit of Tier 2 instruction, were more ambiguous and challenging to interpret. Results of the study and their implications are discussed in terms of tiered interventions in the context of rich vocabulary instruction as well as adjustments to the experimental design which may lend more clarity to future investigations of this important research topic. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com/en-US/products/dissertations/individuals.shtml.]