To get assessed on how well a child knows the subject, the child has to be able to demonstrate how well it knows and understands the subject.
So why should how good someone is at a subject being based on how good they can demonstrate their abilities which relies on communication skills?
Demonstrating abilities through communication is a skill in itself but having to rely on being good at this to get recognition for other skills is a bit like being held to ransom.
Supposing you are good at something but you haven't got good communication skills, then because outsiders cannot see how good you are at your subject they will not recognise your skills and therefore you will get undermined in your skills because of a weakness in communication which is nothing to do with what you are good at.
There should be something which enables the ability of someone with a specific skill to be assessed without having to rely on other communicative skills since it is not a qualification in communication which is being taken so its validity and assessment should not be allowed to be undermined by an external factor.
In the UK with fewer people able to communicate as well as they used to, it looks like many will get underestimated or undervalued for their skills and it will look like we have a skills shortage when we really have a skills recognition shortage.
Think of some people with Cerebral Palsy and other brain conditions who cannot communicate very well with the normal world - some of them are professors in science.
If tests could be performed to find the hidden skills behind the communication problem then we may discover that we have more professors than we ever anticipated but without finding this out it will look like we have more idiots within society.