What you don't understand is the premise of public education. It would have been fantastic for my my kids if their school kicked out the bottom half of their classes. Not so good for two of my kids if the school kicked out the bottom 80 percent. Fantastic for one if the school kicked out the bottom 99 percent.
Physically and mentally handicapped children make it difficult for other children. should they be "kicked out"?
The purpose of public education is to educate the public regardless of their emotional, mental, or physical capabilities.
Teachers who can't educate the kids they have simply don't have the job skills for the job they have.
If a ditch digger needs to be able to throw a shovel full of dirt 6 feet in the air to dig a particular ditch, but he can only manager to throw it 3 feet, then he ain't the one for that job.
Changing the size of the ditch isn't the answer. Changing the ditch digger is needed.