Excessive exposure to the sun's ultraviolet radiation (UVR) contributes to the etiology of melanoma and nonmelanoma skin cancers. Many behaviors that increase lifetime risk of skin cancer--sun exposure, sunburn, and lack of sun protection--occur early in childhood. A 1-day school-based skin cancer prevention effort--Sun Smart Day--was implemented and evaluated in three elementary schools to improve fourth-graders' knowledge, attitudes, and behaviors related to skin cancer prevention. A classroom-based skin cancer prevention lesson was compared to an interactive sun safety fair was vehicles for promoting comprehensive photoprotection. Sun Smart Day interventions had their greatest impact on fourth-graders' awareness and knowledge of skin cancer and children's increased knowledge persisted through the summer break. While both the classroom curriculum and the health fair boosted awareness and knowledge of sun safety among fourth graders, the classroom curriculum demonstrated a slight immediate advantage over the health fair on these outcomes. Also the curriculum was less difficult to implement, but the health fair was more engaging. A Sun Smart Day program may be an important first step in increasing public awareness and understanding of skin cancer and its prevention.