Overseas thematic exposure trips are powerful, eye-opening, and engaging learning opportunities for secondary school students. They encourage young minds to realize and to understand that knowledge is readily available outside the confines of the classrooms and beyond the printed text. The experience these students gain while travelling abroad and being fully immersed in a foreign culture will inevitably change the way they see the world in the present time, as well as their individual lives in the future. One of the core educational values of these enriching overseas thematic exposure trips is the promotion of global citizenship through active engagement in service-learning opportunities for secondary school students. This dissertation is a case study with a quantitative approach from analyzing the results collected from survey questionnaires, as well as with a qualitative approach from several interviews to understand and discover whether the current model in delivering these particular overseas thematic exposure trips (i.e. CAS Week) in an international school in Hong Kong is serving the educational needs to promote global citizenship and to nurture responsible global citizens. The results of the survey questionnaires and the comments collected from the interviews have revealed that the existing programme is a valuable experience for the students at the school. However, the effect of the experience gained from the trips does not necessarily translate into other related long-term service-learning activities to heighten the importance of global citizenship in the school. One of the findings in this case study is the apparent absence of critical and guided reflections to enable the students to understand the value and the meaning in their actions. The students, the teachers, and the alumni at the school do not fully understand the true essence of global citizenship. Hence, prior to designing these particular overseas thematic exposure trips so to educate students about global citizenships as well as maximize their potentials, it is more critical and important for the school to implement all necessary measures, including workshops, professional development opportunities, and training, in order to ensure that all teachers understand the core values in educating global citizenship. Likewise, in addition to these annual trips and other existing regularly held school activities and events, the school must consider allowing additional formal instructional time where students are to engage in dialogues and discussions which allow them to become fully aware of their individual responsibilities in maximizing their own potentials and becoming global citizens. Finally, similar to the recognition given for the achievement in competitive sports and in the arts, there needs to be a fundamental change in the pedagogical understanding to celebrate global citizenship in the school.