We did a graduation meal last year at Cuba Libre. Food was yummy and something different. http://cubalibrerestaurant.com/i/washington-dc/

Wildfire in Tysons does groups very well. I think someone else mentioned Maggiano's but they do a family style menu and you get a lot of food.

I had my graduation dinner (maybe 12 people?) at Old Ebbitt a few years ago. They sat bigger parties out in the atrium, so we had room. And then the whole crew took an evening stroll around the monuments.

Clydes in AlExandria. It is a huge restaurant that can handle a big crowd. I have been there and seen baby showers, bday dinners etc