Strategy instruction during reading can aid metacomprehension producing higher judgement of learning (JOL) and prediction of performance (POP). In contrast, verbal working memory (WM) limitations cause metacognitive deficits and lengthy expository texts impose greater cognitive load. However, impact of cognitive factors and reading lengthy expository texts on the effectiveness of strategy instruction in students remain unexplored. In this study, a correlational design was used and the impact of verbal WM and JOL score on test score was measured. Furthermore, differences in high and low verbal WM on metacomprehension, confidence and prediction accuracy were measured. A total of 105 university students read a long expository text (2578 words) and gave JOL and POP ratings. Then the rereading stage adopted the RAP approach (Reading the paragraph, asking about the main idea, and putting information into words) and self-explanation instructions were given. Finally, students rated JOL and POP then completed a test. Results show test score was significantly higher for high verbal WM than low verbal WM. Verbal WM and rereading JOL score significantly predicted test score. Also, rereading JOL score was significantly lower for low verbal WM. Also, low verbal WM revealed significantly higher POP score and significantly lower study time after rereading. Strategy instruction for long expository text is advantageous for high verbal WM students demonstrating greater metacomprehension, underconfidence, prolonged reading time and effective test prediction accuracy.