"Citizen science" is a great way to engage students in real science in an out-of-school setting. There are many projects in which everyday citizens help scientists by observing the world around them and sharing the data.
One project that starts soon is "Count the Stars," managed by the folks at the University Corporation for Atmospheric Research (a member of the Coalition). From Oct. 1-15, everyone is invited count the stars that they can see and complete a simple form online. This will help scientists better understand light pollution around the world.
Other citizen science projects that are widely used in after-school programs include the Cornell University Urban Bird Studies projects (Consumers Guide review) and the very large and effective GLOBE program.