If students work isn't showing up in the Article Viewer, you can use Wikipedia's built-in diff viewer.

You can use the radio buttons on the History tab of a Wikipedia article to compare any pair of edits (so if your student made several, just select the before and after versions of the page) and use the "Compare selected revisions" button.

Unfortunately, the default version is less than user-friendly, so to get a slightly easier-to-interpret view, go to this link (which is the Beta features tab under your Wikipedia preferences), scroll down to "Visual differences" and enable it. Then click "Save" at the bottom of the page.

Now, when you click on the "Compare selected revisions" button, you should have a pair of buttons to the top right which let you toggle between Visual or Wikitext versions of the diff. The Visual version is much easier to make sense of.