No one ever wants to fire an employee. Especially if he is the sole bread winner of his family. Especially if he/she is a really nice person, well meaning, and trying hard.
But a business has to function, make profits, and move ahead.
And in school, children need to learn. Period.
Every teacher needs to have that first job, and needs someone who believes they have the potential to inspire children and become a great educator. Some schools only hire young teachers after they've proven themselves as assistants or substitutes. Some schools take a chance, and get very lucky - the teacher or rebbi who exudes enthusiasm, creativity, excitement, and thought out lesson planning proves to be a dynamic educator.
And even mediocre can be, ok. If willing to accept suggestions, implement new ideas, and most important, asks for help when necessary.
But it is time for schools to choose the children over the teacher when it comes to really ineffective, poorly trained, unorganzied teachers. I am sure one on one they would be good. Perhaps small groups. Very specific subjects. But if most of the parents are unhappy, most of the kids are not learning, no control going on in class, the time has come to decide the needs of these students overrides the needs of parnossa for the teacher.
(disclaimer: this is in reference to a conversation I had today with a parent, not from any school I work in or have a personal connection to)