Homeschoolers do not demand excellence of themselves. The majority of the homeschooling community operates under a mentality of pride and elitism, generally used to out-performing their public school counterparts. That may be true, but when it comes to art, you still must prove yourself: the fact that you are a homeschooler does not save your art from damnation. Children with very little life experience, very little accumulated skill, and an obsession for Narnia, Middle Earth, Greek mythology, or various period romances, can write a story, call it a novel, and get it self-published. And they are praised for this. Nobody stops them and says, "You have a good thing going. Keep working at it. Eventually you will be ready to publish."
One argument I see against the notion of telling children (my own included) that their work is good but not great is that you may discourage them. Certainly if grace and courtesy are not employed, and the artist's heart is not in the work, a permanent discouragement may set in. You cannot make someone endure the race. But sometimes encouragement does not look like blind accolades. Sometimes it is constructive criticism both in regard to the work and in regard to the artist.
People do not demand excellence. I am not sure why: fear, perhaps, of the time and sweat it will take to make excellence a reality, and possibly a confusion that to dismiss sub-par work is to dismiss the artist as a person as well. But you do not owe it to the writer (you do not owe it to me) to like the book. It is not a direct attack upon my character, it is your judgement (hopefully made with a sound mind and with reason) upon the art. If you are not willing to cull the tares from the wheat, the only person that reflects badly upon is yourself, not the artist. Demand excellence.
There is a fear of producing excellence - not that I am afraid of it, but that I am afraid I will not achieve it. But I have noted that both Beowulf and Bilbo Baggins were put in the situation of going to confront a dragon, only in the former's case there was no fear, and in the latter's case there was profound fear - and yet a determination to go on in spite of trepidation. Bilbo Baggins is the better of the two. I am deeply, acutely afraid of falling short of excellence. Occasionally I write something brilliant, oftentimes I just write passably. But I go on, and I keep fighting, and I actually owe it to myself and to my readers to make sure what art I produce comes level with, or exceeds the level of, excellent art already created and established. In this middle-class, plebeian society, there is a lack of an aristocratic demand for good products. The homeschool community often seems to be a bastion of this laissez-faire attitude toward writing. This is not universal, but it is common enough that I was glad when Suzannah Rowntree pointed it out by way of warning.
When you commit to being a writer, you are no longer a homeschooler. Homeschooling has nothing to do with writing. Once you enter into the world of writing, you are entering a pantheon full of names that could easily crush you. It is far better to enter it humbly and to work hard, and to strive to achieve the highest standard of excellence that you can, than to whip off a story, get a cover for it, and pop it on a Kindle so that the world can see the "achievements" of another "homeschool author."
for inspiration, you can always watch "whisper of the heart"