Reading research over the past 20 years has greatly advanced our understanding of reading problems. We know that many children who experience difficulty learning to read have phonological processing weaknesses (e.g., Liberman, Shankweiler, & Liberman, 1989) and poor word recognition skills (e.g., Ehri, 1998; Share & Stanovich, 1995). Moreover, a number of researchers (e.g., Blachman, Ball, Black, & Tangel, 1994; Byrne & Fielding-Barnsley, 1991; Fuchs, Fuchs, Thompson, Svenson, Yen, Al Otaiba, et al., 2001; Torgesen, Wagner, & Rashotte, 1997) demonstrated that programs emphasizing phonological awareness and decoding can significantly improve young students' reading achievement, at least in the short term. Yet, there is a persisting problem: Not all children respond well to even the most effective interventions. Researchers have reported that 20% to 30% of children at risk for reading difficulties (see Torgesen, 2000), and more than 50% of children with disabilities (e.g., Fuchs, Fuchs, Thompson, et al., 2001; Torgesen et al., 2001) do not respond adequately to generally effective early reading intervention. Such students have been dubbed nonresponders. Recently, responsiveness-to-intervention has been suggested as an alternative to the current IQ-achievement discrepancy approach for identifying students with learning disabilities (e.g., President's Commission on Excellence in Special Education, 2002). This has contributed to researchers' interest in finding the best ways to identify nonresponders and develop effective interventions to reduce unresponsiveness (e.g., Case, Speece, & Molloy, 2003; O'Connor, 2000; Speece & Case, 2001; Vaughn, Linan-Thompson, & Hickman, 2003; Vellutino et al.).
