The purpose of this study was to investigate the effect of Cooperative Learning with a Dual Situated Learning Model (CLDSLM) and a Dual Situated Learning Model (DSLM) on (a) conceptual understanding (CU) and (b) scientific reasoning (SR) among Form Four students. The study further investigated the effect of the CLDSLM and DSLM methods on performance in conceptual understanding and scientific reasoning among students with different motivation levels. A quasi-experimental method with the 3 x 2 Factorial Design was applied in the study. The sample consisted of 240 stu¬dents in six (form four) classes selected from three different schools, i.e. two classes from each school, with students randomly selected and assigned to the treatment groups. The results showed that students in the CLDSLM group outperformed their counterparts in the DSLM group—who, in turn, significantly outperformed other students in the traditional instructional method (T) group in scientific reasoning and conceptual understanding. Also, high-motivation (HM) students in the CLDSLM group significantly outperformed their counterparts in the T groups in conceptual understanding and scientific reasoning. Furthermore, HM students in the CLDSLM group significantly outperformed their counterparts in the DSLM group in scientific reasoning but did not significantly outperform their counterparts on conceptual understanding. Also, the DSLM instructional method has significant positive effects on highly motivated students’ (a) conceptual understanding and (b) scientific reason¬ing. The results also showed that LM students in the CLDSLM group significantly outperformed their counterparts in the DSLM group and (T) method group in scientific reasoning and conceptual understanding. However, the low-motivation students taught via the DSLM instructional method significantly performed higher than the low-motivation students taught via the T method in scientific reasoning. Nevertheless, they did not perform significantly higher in conceptual understanding. Finally, the results showed that there were no significant interaction effects between student motivational levels and instructional methods for the scientific reasoning and conceptual understanding scores.