The aim of the present study was to investigate the effects of an intervention on students' achievement and motivation. The intervention was in the form of an instructional approach named Dual-Approach Instruction since it was designed to facilitate both the cognitive and non-cognitive aspects of students' learning. The intervention effects were assessed through a cluster-level assignment design, which compared the control and intervention groups' achievement and motivational outcomes. A total of seven teachers and 427 grade 7 students participated in this study. Four teachers were assigned to the intervention condition and participated in a series of workshops on Dual-Approach Instruction. These teachers then applied the intervention to two topics, Speed and Density, with 231 students. The rest of the teachers and students were in the control group. Multiple regression analyses of students' achievement and motivation pre-test and post-test scores indicated that the intervention had a significant effect on students' achievement in complex problem solving, as well as in the following six motivational attributes: self-regulation, engagement, sense of competence, task goal orientation, education aspiration, and career aspiration in science. The results suggest that Dual-Approach Instruction benefits students in terms of dual outcomes: science achievement and motivation.