What percentage of F's in a class is it reasonable to give?

What percentage of F's in a class is it reasonable for a teacher to give? I mean what's the dividing point between a teacher firmly drawing the line at demanding minimum competency and rigor, and a teacher who is simply not reaching their kids and flunking so many students that we clearly see that the educator is actually ineffective at their job?

If 80% of the kids in a class are failing a class, is the teacher not a part of the problem for the immense amount of failure in the room?

What about a teacher with a 12% failure rate?

A 45.6% failure rate?

Heck, NCLB takes graduation rate into account when it assigns us our AYP and API scores in California so if we do not graduate 100% of our kids, we, by nature, are penalizing ourselves.

Makes a nice case for grade inflation doesn't it? Or going after teachers who flunk too many kids.

But some teachers are flunking too many kids. Or, I should say, "have too many kids flunking their class".

So what's the acceptable number? Is it zero? That seems unreasonable. Is it 79.9%? That seems excessive.

Is there anyone who can provide guidance on this type of thing?

A Bell Curve with 10% A's, 15% B's, 40% C's, 15% D's and 10% F's is how they drew it up in the theory class I took once upon a time. But my own classes NEVER balance out like that. Not even close. (And seldom do any of the theory classes offer things that truly measure up where the rubber meets the road.)

So if we want to raise our AYP and API score, the method is simple -- flunk less kids.

And don't think that teachers aren't having the screws turned to do so by admins who care more about "school ranking and scores" than student learning.

Because in the world of our current educational dysfunction right now, student learning and higher AYP and API scores are often at odds.

So, I ask again, how many F's is a teacher allowed to reasonably give?