But here were assessing written and spoken English, these are two very different things. Colloquialisms through speech I personally don't mind, as it is quicker (more lazy if you wish) and sometimes better understood...minus the constant use of the word 'like'.
Standard written English IMO is a must. In fact in our secondary school, if you could not write standard English you would never excel. I remember receiving 90+ percent in 12 out of 13 subjects 3 years running, but between 55%-60% in English. I was kept at a mid tier level, which meant at GCSE level, grade B was the highest you could achieve.
Along came my Jamaican tutor, who taught myself at 15 how to construct a proper sentence, as well as reading professional papers, the dictionary and thesaurus. After one year with her I was pushed up a group so I could sit the higher paper. Our English lesson at school involved watching the Euros with a coat hanger stuck in the back of the TV, or comprehension of the basic sort. I was shocked, as was my tutor when I didn't know the difference between an adverb, conjunction and noun.
Bit of an addition to show its not always down to the pupil; GCSE time, in a high tier group, still with my Jamaican boudica. I was receiving C and D grades for my examination coursework. My tutor who was now the inter relations between America and the UK for scholarships, decided this was not right so came to my school with several external examiners and journalists, sat down with the head of year and my English teacher. The next week my English teather quit amid reports of favouritism. I went on to get an A*/A in literature and written English respectively. Unfortunately my head of hear was my Geography teacher, following the previous investigation my Geography mark dropped from an expected A* to a B. I was expecting this as the ogar was quite peeved.
Geography coursework was undertaken in Aberystwyth counting and mapping every shop on the high street. So probably came across a few guys here albeit with bum fluff as a beard at 15.
Furthermore, when we receive prescriptions written by doctors without a basic understanding of standard English, it is extremely sad. I would expect this to be a necessity, unfortunately it is not you need a minimum of a grade C or pass in some cases, in English, to become a Doctor.