Background: Being able to think independently is a must for students to construct new knowledge in their minds. Self-explaining is a constructive learning strategy that encourages students to think for themselves and to make inferences that go beyond the given information. The Self-explain--Discuss--Re-explain (SDR) strategy adapted from self-explaining is expected to be able to help students learn science and foster the habit of independent thinking. Purpose: This study employs a quasi-experimental design to investigate the effects of SDR and traditional strategies on high- and low-achieving fifth-grade students' achievement in learning about the position and motion of the sun. Participants: Altogether 104 students participated in this study, with the 52 receiving the SDR strategy designated as the experimental group, and the other 52 receiving the traditional strategy designated as the comparison group. Each student was classified as a high- or low-achiever based on their test scores from the final science exam the previous semester. Design and methods: The research instrument for this study was a two-tier multiple-choice test. We used this test for both pre- and post-tests of the experimental group and the comparison group, and then performed statistical analysis on the data obtained from the pre- and post-tests. Results: The findings show that the SDR strategy was more effective at helping high- and low-achievers learn about the sun's position and motion and in helping close the achievement gap between them than the traditional strategy was. Conclusions: The SDR strategy can help low-achievers catch up with their high-achieving classmates. It can be used to remedy low-achieving students' weaknesses in a specific area of science.