Background: Students need to practice their hands-on skills when they are young to develop confidence for their future careers. Nowadays, iSTEAM (integrated science, technology, engineering, arts and mathematics) contests provide opportunities for participants to experience meaningful and challenging hands-on tasks that may foster learning, and to generate positive attitudes that may enhance their self-confidence in their ability to make miniature models. Purpose: To understand the relations between mastery orientation of hands-on tasks, hands-on making interest, engagement, and self-confidence enhancement in an iSTEAM (integrated science, technology, engineering, arts and mathematics) contest. Sample: The sample consisted of 212 junior high students including 131 males and 81 females who were preparing to join the iSTEAM contest. Design and Method: Data were collected from 212 questionnaires and subjected to confirmatory factor analysis and structural equation modeling using AMOS 20. Results: The results indicated that mastery orientation of hands-on tasks was positively related to hands-on making interest and engagement. Engagement was positively related to hands-on making interest, and hands-on making interest and engagement were positively related to self-confidence enhancement. Conclusions: Students with high levels of mastery orientation might gain higher self-confidence, mediated by their interest and engagement in a science and technology hands-on making contest.