This article describes a randomized controlled trial conducted to evaluate the effects of an intensive, individualized, Tier 3 reading intervention for second grade students who had previously experienced inadequate response to quality first grade classroom reading instruction (Tier 1) and supplemental small-group intervention (Tier 2). Also evaluated were cognitive characteristics of students with inadequate response to intensive Tier 3 intervention. Students were randomized to receive the research intervention (N = 47) or the instruction and intervention typically provided in their schools (N = 25). Results indicated that students who received the research intervention made significantly better growth than those who received typical school instruction on measures of word identification, phonemic decoding, and word reading fluency and on a measure of sentence- and paragraph-level reading comprehension. Treatment effects were smaller and not statistically significant on phonemic decoding efficiency, text reading fluency, and reading comprehension in extended text. Effect sizes for all outcomes except oral reading fluency met criteria for substantive importance; however, many of the students in the intervention continued to struggle. An evaluation of cognitive profiles of adequate and inadequate responders was consistent with a continuum of severity (as opposed to qualitative differences), showing greater language and reading impairment prior to the intervention in students who were inadequate responders.