If you happen to be extra passionate about the teaching profession, please share your knowledge by asking general questions in the Educators' forum—before writing an email—so that your question can help others in a similar situation [ remember to search first! ;) ]. Since this is the place for staff, parents, teachers, and helpful Duolingo community members to hang out, it is likely the absolute quickest way to find and get help.
If your question or comment is about a specific language or course, please ask in the appropriate forum. If or your students you are having issues with Duolingo itself, please search and ask in the Troubleshooting forum.
Contact Duolingo for Schools privately: Send stories, lesson plans, pictures, class letters and/or ask for help that requires the exchange of usernames and/or other sensitive pieces of information by writing to: firstname.lastname@example.org.