Not quite sure where this should go in the docs, but semi-regularly a class gets assigned to contribute to open source projects (awesome!) and then everyone gets a little frustrated (not so awesome), so I think we should add some guidelines to the docs (maybe in the contributing guide somewhere?). Something like

Guidelines

Thank you for encouraging your students to contribute to Matplotlib. To make this a productive experience for everyone, we ask that you please:

1. Inform us at least <a week?> in advance, via either gitter, discourse, or the matplotlib-dev mailing list. (I don't want this to just be a @tacaswell gets an email thing)
2. Email a class roster of github usernames to matplotlib@numfocus.org (or some other method of confidentially sharing the information)
3. Help us curate a set list of issues that you think are appropriate for your students. With enough notice, we may even be able to create a project specifically for your class.
4. Verify that your students have read our contributing guide. They can ask questions on discourse
5. If you have more than 50? students, please provide the github handle of at least one person we can assign to review the student contributions.