What is the best way to attract the most birds in a small amount of time?

I am a senior in a high school where it is common for senior pranks to happen. My senior prank involves having a bunch of birds be in the main lawn area of the school. The problem is is that I need a bunch of birds to show up, but they need to show up in a short amount of time for this to work. I would prefer the solution to be cheap but if not cheap at least affordable for a high school student making minimum wage.
Answers

Anonymous

If you spread food or anything, be fully prepared to clean it up afterward. They will know exactly who did it, since you posted this on a public forum.

KY-Clay

Sprinkle out lots and lots of bird seed about 1 hour before you want them there. Spread it and they will come.