Differing etiological explanations have been proposed to account for poor comprehenders’ difficulties with reading comprehension, with some researchers emphasizing working memory deficits and others arguing for oral language weaknesses playing a key causal role. The authors contrasted these two theoretical accounts using data obtained from direct measures of working memory and from teacher ratings of poor comprehenders’ behavior in the classroom. At the group level, poor comprehenders showed weaknesses on verbal but not nonverbal working memory tasks, in keeping with the "language account." However, they also showed evidence of elevated levels of problem behaviors specifically associated with working memory deficits. Further analysis revealed that these group differences in working-memory-related problem behaviors were carried by a small subgroup of poor comprehenders who also displayed domain-general (verbal and nonverbal) working memory problems, argued to be reflective of "genuine" underlying working memory deficits.