Key stage 2 and 3 speaking and listening is assessed in every school in England that follows the National Curriculum
The way we speak greatly influences the way other people treat us. If we mumble and use lazy speech we give the impression that we don't care. If we speak clearly so that people can hear us, we tend to get treated with more respect.
This applies to children at school with teachers as well as outside of school with shop keepers, dance teachers, soccer coaches etc.
It's a fact of life that any child who has good clear speech has a head start in life!