In the past years, there has been an interest to map and characterize the architectural engineering and the lighting design programs at the School of Engineering, Jönköping, Sweden. The investigations revealed issues related to student's self-efficacy and locus of control. This study aimed to create a routine for solving design problems by planning a small individual design exercise as a mental reward mechanism for students to boost their self-efficacy and internal locus of control. It was hypothesized that internal locus of control correlates to an increased self-efficacy level. The study objectives were (1) to propose an interior design exercise on problem-oriented learning that fits in the overall curriculum of Architectural engineering and Lighting design programs at the undergraduate level. Also, (2) to assess students' locus of control and status of individual preference for problem-solving approaches and self-efficacy. The interior design exercise lasted for a month in February 2020. With the outbreak of the COVID-19, the interior design exercise was the only design exercise held. Altogether, sixteen students completed the workshop. The pre- and post-evaluations show that a single design exercise had slightly shifted the students' locus of control to more internal, which indicates a more self-controlling behaviour. Also, an increase in the enjoyment of a design exercise was recorded, and students demonstrated a slight preference shift towards a less defined and more open design exercise. Students' internal locus of control correlated to self-efficacy measures in the pre-intervention phase but only showed a tendency in post-intervention. The design workshop teacher's reflection on the participants' design process revealed that many worked in groups, which might decrease the self-oriented decision-making rating for self-efficacy. The future investigation would extend these design workshops' complexity by involving a set of lighting design, architectural and urban space design exercises for a more comprehensive review of the effects.