If you’re referring to those little cardboard things on tissue/cereal etc. boxes then I just dropped off a bagful at:
West Education Campus
1338 Farragut Street NW
Washington DC 20011
They have a collection box right in the lobby, next to the guard’s desk. Don’t know how they fit into the DCPS needy-ness pyramid, but they at least knew what I was talking about when I called, unlike my local establishment -Shaw Junior High.