There are teachers who can't teach, there are teachers who can teach but are too lazy/tired/ washed up and there are many teachers who can but struggle to do so consistently due to the challenging behaviour in the classroom.
I have a teacher in my department who works hard and with the right classes is a good teacher. However, this teacher can struggle with some classes and the results for last year's GCSE cohort was not good. So this teacher is on an informal capability procedure. Now I have no problem with removing bad teachers but I have a real problem with using such a blunt instrument on struggling teachers. Before I became a teacher I worked in business for 10 years and came across 100s of workshy, lazy and incompetent people. Yet I never knew of anyone who was put on any kind of warning for their performance, they simply didn't get pay rises and soon either improved or moved on. I find it remarkable that schools try to use such blunt instruments as capability so quickly, because as soon as something goes on your record that's your career as good as over.