is an effective method to help young people become contributing members of society.

　　Although there is enough proof from both small and large assessments that after-school programs can make a positive difference, it is important to note that not all programs are equal.

　　First, dosage（时量）matters -young people who attend the most hours over the most years benefit more than members who attend less often or over a shorter period of time. Next, after-school programs make a bigger difference for those students who need help most and have the fewest choices. Finally, program qualities matter. After-school programs work best when they create unique opportunities for youth. They should provide opportunities, skill building meaningful involvement（参与）, expression suggestion, service, and work. Staff characteristics make an important difference in the quality of a program. The adults should treat youth as partners, create safe and fair environment, encourage personalized（个性化的）involvement, and actively create learning opportunities. In short, although after-school programs have promising future, how they are designed and run matters.