Scholars are calling increasingly for educational reform to embed meaningful out-of-class events in the current curriculum, in order to enhance students' generic competency development. Towards this goal, featuring self-confidence as an important generic competency, this mixed-method study explores key characteristics of extracurricular activities that lead to enhancement of students' self-confidence. Based on an extracurricular program designed for developing students' generic competencies, including self-confidence, questionnaire data was collected from 423 secondary school students in Hong Kong alongside 133 reflective journals. Four important activity characteristics--i.e. authenticity, being challenging, expressivity and reflectivity--have been identified to inform future activity and curricular design.