The purpose of this research is to develop a problem-oriented science toy curriculum, and to explore how learning by teaching strategy influences students’ learning. The participants included 18 5th graders in an elementary school of Pingtung. During the treatment, students were randomly assigned in a group of two and designing their rubber bank car. On completing the car as well as worksheet, they were asked to have their car run over five meters. If failed, they needed to improve and repeated the test. Those who passed the test were required to shoot a teaching video about how to make a rubber band car. Finally, each one took a post-test and a four-week delayed test. The results of Wilcoxon Signed Rank Test (Wilcoxon Signed Rank Test) did not reach a statistically significant difference (Z=1.15, p > .05) between the post-test results and post-delay test results, suggesting that combining learning by teaching strategy into the PBL rubber band car activity can help students’ learning performance, such as the retention of cognitive concepts.