If it is anonymous and unfiltered, it is possible to shit-spam it. Write some server that can find proxies and write random words from dictionaries to fill up so that it becomes impossible to filter the mean from the nonsense. Gotta take them by their game ! However, if it grows with too many people that have the free time to post (ala 4chan) this strategy becomes too difficult. For a highschool, shouldn't be too difficult ?

Btw, I don't know the specifics of the "app", but it could be done, even, with basic captcha imo.