Life imitates Gossip Girl tonight as the teens from six of the city's most elite private schools join together for a prom in the Waldorf's Starlight Roof (the Waldorf ballroom is where public high school Stuyvesant's prom will be this Friday -- ground floor for the plebes!). The NY Sun reports on the gala event, which will bring together a privileged pack from Collegiate, Browning, Brearley, Hewitt, Spence, and Nightingale-Bamford schools. Dinner, dancing and silver-plated......