Take Route 27 (Nassau Street) north past Harrison Street to the next traffic light, at Snowden Lane/Riverside Drive.
Turn right at the light onto Riverside. The school is on your left after a few houses.
Take Route 1 south to any convenient connecting road that will get you onto Route 27 south (such as Raymond Road). After you leave Kingston and pass River Road and Lake Carnegie, the next traffic light is Snowden Lane/Riverside Drive.
Turn left at the light and look for the school on your left after a few houses.
The Suburban Transit bus between NY and Princeton travels along Route 27. You can take this bus south from the Port Authority bus terminal in Manhattan, or north from the intersection of Nassau and Witherspoon Streets in Princeton (tickets available at the Palmer Square kiosk). Buses run twice an hour in each direction.
(Thanks to S. Lorand for directions. Map to follow ...)