One effective way of keeping students motivated is to show them that their work is appreciated. You can do that by using WikiLove to give out awards whenever you see outstanding work—and encourage the students to do the same for each other.
You can go to a student's userpage and click the heart icon to bring up the WikiLove tool. Select what kind of award to give them, add a personal message, and it will be added automatically to their talk page.
This video gives a little bit of background on barnstars, the traditional symbol of appreciation for good work on Wikipedia, and shows how to award them with WikiLove. For many Wikipedians, barnstars in particular are a source of pride.