Allow me to play devil's advocate here.
Tallahassee Classical School has made the news as far away as Australia because its principal was pressured to resign over (among other issues) an art lesson that included an image of Michelangelo's famous statue of David, which upset some children and parents. And once again, Florida, and those who objected to the photo, are being demonized because of it.
Don't get me wrong. We haven't made it to Florence yet, but you can bet David will be high on our list to see when we do. And if you're going to study classical art, you are going to run into a lot of images people could object to. Naked women, for example, are a whole lot more common than naked men. Rape, orgies, wars, graphic violence, eroticism, prejudice and "hate crimes"—it's all there, because great art reflects reality. Granted, it's far more tastefully done than what comes out of Hollywood, but still, it's there.
That said, there is SO much great classical art available, that were I teaching an art course to sixth graders, I'd probably leave that one out. Unfortunately, sixth graders are an age group that cannot be trusted to be mature about anything involving naked body parts or bodily functions. I remember how my own class of about that age reacted when a parent came into school and shared slides of his recent trip to Europe, including the famous Manneken Pis.
Unless you are choosing to be provocative, David is hardly necessary in a child's brief introduction to art.
If I had to choose one sculpture to represent Michelangelo, it would probably be his Pièta—but you can run into controversy there, too. Would people be so down on the parents if they had objected to the image for religious reasons, as some surely would have?
There's the point: different parents will find different things too objectionable to teach their young children. Which is why the school, very intelligently, had instituted the policy that parents are to be allowed to see the curriculum materials, and must be notified of anything that might be considered controversial. A blanket statement at the beginning of the course, something like the following, would have prevented a great deal of stress and misunderstanding:
This is a course in Renaissance Art, and as such will feature a great deal of Christian and Classical imagery, including religious themes, graphic violence, and unclothed people. We believe these works of art to be of sufficient importance to include them. Parents are welcome to view the materials and have their children excused from lessons they believe would be harmful.
I would hope for something similar with regard to music. You cannot study great Western music without including the music of the Christian Church; many schools no longer try, for fear of lawsuits, thus eviscerating their choral programs. Explain up front why you are including these great works, allow parents to excuse their children if they disagree—and get on with the job.
The school (on the advice of their lawyers, of course) is not giving any details about why the principal was pressured to leave. But I suspect it was less about the actual content of the class and more about violating the policy of not leaving parents in the dark.
One more point: most objections I hear against the parents who did not want their children to see the materials are mocking them for not being comfortable with pictures of naked bodies. That is, the parents are upset about something that their detractors have no problem with—which to my mind delegitimizes the objection. Everyone has something they consider out-of-bounds for being taught to their children; we should image that, instead of what we have no problem with, as the issue here.