We do that too, but for more like 500. We do it a variety of ways at our 5 high schools. One year we took over the downstairs of the school, the halls, kitchen, mall and gym. We parents made sets, and none of the original walls were visible as they were all covered with decorated flats of a western town, the can-can girls on stage, the jail, etc. We rent lots of special games for the kids, and do special food too. Though I think most of them arrive full from their family's graduation feast. They rent huge, padded sumo wrestling outfits, for the kids to wear. The rent snow cone or slurpy machines (it gets hot with so many kids in the place.) Human bowling. Fortune teller. Wedding chapel and wedding license. Karioke room. Casino games such as 21, roulette, etc. and play money for each kid and prizes to purchase with their winnings at the prize booth. Baloon basketball. All sorts of games and contests. In one small room we put down wrestling mats for the sleepy ones. A money booth--wind blows money and whatever they can get in one minute they keep--real money mixed with fake. Food of all sorts. Underclass parents man the event, but senior parents fundraise and build it. That way, no kid is partying with his parents peeking around as chaperones--they are someone else's parents.