Rush is generally only available for non-soldout performances. It would appear likely that the entire run of this show will sellout within a day or two so I can't imagine a lot of rush seats being available (perhaps if there are cancellations or returns).
I don't know much about The Public's student ticket policy other than you have to buy tickets in person at the box office with a valid ID -- two tix per ID. If you want to go that route (and they allow you to buy student tix in advance and not just rush day-of), it would behoove you to be at the Public Theatre box office on Monday the 19th at 1pm when it opens with your ID (it closes at 6). I could be wrong, but I doubt that there will be a lot of tickets left (for students or anybody else) much past Monday.
"What a story........ everything but the bloodhounds snappin' at her rear end." -- Birdie
[http://margochanning.broadwayworld.com/]
"The Devil Be Hittin' Me" -- Whitney