I suspect that the descriptive/prescriptive divide is a particularly contentious one in the world of children's literature, because it depends on basic philosophical differences about what stories should do.
Some think that stories should reflect the world as it is, and should give kids a safe place in which to think through challenging situations. To ask themselves, "What would I do in that situation? Did the characters' actions work for them? Why or why not? What else could they have done?" This is the descriptive school.
Others think that stories should reflect the world that ought to be, and should give kids a safe place that represents the ideal situation. This is the prescriptive school, and its adherents tend to be more concerned with concepts such as role models.
An author of the descriptive school might write about a character with, say, a drug addiction, while a prescriptive author might shy away from including such a character. In real life, both authors may be equally opposed to drugs. The prescriptive author might say that kids need to be protected from all mention of drugs, for fear of glamorizing them. The descriptive author might believe that kids need to be protected from real drugs, but that stories in which characters encounter drugs are useful in helping readers figure out what they want to do when they're eventually faced with the real thing.
Another way to look at it: Prescriptive authors may think the world is tough enough, and books should provide a pleasant haven from the grit of real life. Descriptive authors may think that readers are comforted to know they're not alone in sometimes having negative thoughts and feelings, scary experiences, tough challenges.
My own writing tends to fall into the descriptive school, but I think it's useful to have both kinds of books on our shelves.
