Using two intact offerings of an engineering course for a treatment class and a comparison class at a U.S. university, the current study examined the effects of instructional interventions on students' self- and peer-assessed intercultural competence while completing a group design project. Undergraduate students enrolled in a semester-long engineering design course were required to work in mixed national groups, assigned by the instructor, in and outside the classroom. Students in the treatment and the comparison classes completed initial and exit assessments of an adapted Intercultural Effectiveness scale. The treatment class was also presented with three modules on cultural relativity, cross-cultural communication differences, and diversity in workplaces. At the end of each of those instructional sessions, the students completed critical reflections in response to given prompts as to what they had learned. Analysis of the quantitative data suggests the impact of structured interventions on students' introspective awareness of cultural differences and uncertainty about how to deal with such differences, which was validated by qualitative reflection data illustrating students' acknowledgement of intercultural differences during completion of a group design project. Findings highlight the benefits of forming diverse groups for engineering design projects, allowing students to gain practical experience while collaborating with classmates.