The purposes of this study were to (1) examine the effect of cooperative-learning summarization instruction for sixth graders in order to learn the influence of long-term, explicit instruction, and to (2) evaluate the students summarization ability by the two-stage summarization assessment. Two intact classes (3) students in the experimental group and 32 students in the control group) in an elementary school were recruited from Chiayi City. For the experimental group, students received one-year cooperative-learning summarization instruction, whereas for the control group, students received traditional literacy instruction. The results showed that students who received the summarization instruction outperformed those who received traditional instruction on the immediate and the delayed measure. In addition, the intervention effect was also found on the quality of students summarization.