The study investigated the effect of using design thinking approach in STEM learning context on optimizing students’ retention of achievement in difficult physics concepts. Study was carried out in an afterschool environment which necessitated the researcher using a single group quasi experimental research design conducted in purposively selected secondary schools. Intact classes of physics students comprising of 48 male students and 41 female students overall were used in the study. A 25 item Physics Learning Achievement Test (PLAT) used in the study was validated by experts in STEM fields at pilot test. Reliability coefficient of validated PLAT using test retest method by Kuder-Richardson (KR-20) was established at 0.86 for the multiple choice test and Pearson product moment reliability coefficient for the semi-structured questions at 0.81. The modules combined the elements of STEM learning and design processes of empathy, ideation, brainstorming prototyping, testing and retesting to learn selected physics concepts for three months. Prior to its use, students were administered a pretest and a posttest after the study intervention using PLAT. A delayed-posttest was later administered to participants after two weeks of posttest using PLAT. Result obtained from statistical analysis using the paired sample t-test and a one-way ANCOVA revealed that there were no significant differences between the posts –test and delayed post-test of mean score of achievement in physics learning for male students as well as for female students. Conclusion and relevant recommendations were therefore made in the study.