A subset of students fail to respond adequately to reading interventions. This synthesis systematically reviews studies in which students in grades K-3 responded inadequately to a Tier 2 reading intervention and were provided with a Tier 3 intervention. Descriptions of the Tier 3 reading interventions and effects are provided. To meet inclusion criteria, studies were required to (a) provide documented, multi-tiered reading interventions with at least one reading outcome measured; (b) include students in grades K-3 who previously responded inadequately to a Tier 2 intervention; (c) use experimental, quasi-experimental, or multiple-group designs; and (d) be peer reviewed and conducted in English. Twelve studies met inclusion criteria. Results demonstrate that students who responded inadequately to Tier 2 interventions can make significant growth from Tier 3 interventions compared with a control group of peers who were also inadequate responders, but often fail to catch up to their more responsive peers.