What is the percentage linguistic retards

All English teachers probably know this problem.

You got a nice job one class and 20 kids but after two to three month you discover that you have one ore even two kids in your class who won’t learn anything.

They can’t even catch three words and their pronunciation is unrecognizable.

Suspected reasons are many

Memory

Sound recognizing

Sound recognizing speed

Bad hearing

Control of the tongue

Word finding difficulties etc.

Now I want your numbers.

Mine are 1 to 2 out of every twenty students perform very badly. They cannot learn the second language in a group class environment. Two in twenty are linguists they learn the language no matter how poor your teaching performance or how bad the classroom environment plus schools management etc.