Evaluating how participating in various experiences affects young people is important to promote further participation in community practices. We examined the effects of participation on junior-high school students’ self-efficacy and motivation towards community-improvement activities: of 114 students from a junior high school (Study 1) and 10 voluntarily participated in a park-design project (Study 2). The experience of participation even in small-scaled contributed to increasing the self-efficacy of the participants and especially enhancing their motivation with regard to community empowerment.