Q. What are the best plants for outdoor stormwater container gardens for urban schoolyards?
It's hard to know from your email what kind of outdoor stormwater container garden system you have in mind. Were you thinking of a flow-through planter such as the one shown here in this PDF?
Or did you have something else in mind? Have you looked into the Philadelphia Water Department's Raincheck program? Take a look at the links showing Green Home Projects - you will see how tos for
as well as other projects. Downspout Planter project includes some plant recommendations.
You may want to look into this program. Good luck.