Yes, it is absolutely necessary. My classes meet every two weeks, and that is much too long for a student to go without oversight. Actually, even one week is too long.
The oversight of the Editor is one of the most important aspects of Writing to Learn classes. It is possibly the top reason that my students are so successful in their writing. Conversely, my few students who for some reason do not receive consistent Editor oversight usually flounder and fail to progress.
Understandably, many homeschool parents want outside classes that give them a break from teaching; however, all of my students must have a parent who commits to serving as Editor.