Members ask under each lesson; you answer and review their work.
Under every lesson, members can ask questions and leave comments. You get a notification for each new one, and Lesson Q&A and assignments lists the ones waiting for you first. When you answer, the member gets a notification and an email. You can pin, hide or delete posts, or switch comments off.
Assignments: give any lesson an assignment (a written answer, a file, a link, or any of these). Tick Needed for the next lesson and the next lesson stays shut until you approve their work. Review it in the same place: approve, or send it back with feedback. Either way, they're told.