Art classes should be a requirement in every schools curriculum, not an option. There will be 3 phases, which end in a mentor program and project that uses concepts to prepare the students for college.
Kids minds always wonder. They are still trying to figure out the world and how/why everything works the way it does. With the proper resources, a non restricted environment, and people who care; kids can cultivate their creative challenge.
I really like your idea. As far as the problem of getting access to young groups, you could try places like the Boys and Girls Club, The Urban League, or other after school programs who are very flexible with their schedule. I also teach for Junior Achievement, who have day long sessions where you may have the opportunity to incorporate your lesson in there.
Also, I think it may be best to start students with a project that they are interested in before giving them harder ones. I remember being in school and when something was super hard I would get uninterested in it if it was not for a grade. If they can see it as a fun project first, then they will be more inclined to look at the next one as a challenger if its harder or not what they are use to. You have to be realistic about getting these students to participate. Maybe have "study snacks" included?
If there were some way you could get support from teachers to offer this idea as a project for extra credit for the class that would be great. The benefit with this is that you would not necessarily have to provide a token. The drawback of using extra credit as a reward is not getting genuine participation from students.