For revising an existing article, consider drafting the first significant edits (e.g., a new or heavily revised section) in a sandbox. This is more effective than fully rewriting an existing article in a sandbox, then replacing the article all at once, which may antagonize other editors.
If you use a sandbox, you should place a notice on the talk page of the article with a link to the sandbox. This allows interested editors to post suggestions to the talk page before work starts. Once you are happy with the draft you can place another notice on the talk page of the article with a link to the sandbox, asking for comments before editing the article itself.
Your role as the expert
The sandbox stage is a good opportunity for you, as their instructor, to highlight major problems and point students in the right direction to fix them. Make sure students are using high-quality sources, and make sure they are rewriting information in their own words rather than copying the sources or committing plagiarism through close paraphrasing.