I took the basic keel boat
course at this place on City Island, Bronx, NY over 5 years ago and found it to be well run: New York Sailing Center & Yacht Club: sailing school, club and marina.
At that time they were using Benetteau 21's which I think they still have.
There are also outfits at the Chelsea Piers (Sailtime, which uses Hunters), NY Sailing Club (which have mostly Solings) that offer the 'basic keel boat' courses in either ASA
or USS(?) certification