A study examined whether previous knowledge facilitates the acquisition of a reading comprehension strategy by children who are poor readers. Subjects, 54 fourth- and fifth-grade boys in Palm Beach County, Florida, who were poor readers and baseball experts, were trained in the use of a reading strategy (asking "why" questions), with instruction being embedded in baseball (T-BB) or nonbaseball (T-NB; about less familiar sports) stories. The boys were tested 1 to 3 days after training, then again 2 to 3 weeks after the training. Boys in the T-BB group demonstrated greater strategy use at both posttests, indicating that knowledge base aided in the acquisition of a reading comprehension strategy. More "why" questions were asked by the T-BB group for the less familiar nonbaseball stories, an indication of appropriate monitoring. Children with higher declarative metamemory scores demonstrated better strategy acquisition and recall (both free and cued recall) than did boys with lower metamemory scores. (Three tables and four figures of data are included.) (Author/RS)