noble You asked which school teaches English for 5-6 hrs a week then you say your school teaches it for 4. I call that splitting hairs; it's one hour difference!
In any case, those 4, 5 or 6 hours are not spent on basic literacy skills like phonics, reading and comprehension- far from it. That goes out the window from year 7 (apart from comprehension.) For most of the lessons, there is no focus on spelling, reading skills etc.
What you ought to be getting upset over is the fact that Jack was failed by all his UK schools.
I taught for 40 years in state, indy, day and boarding schools, special schools for children with severe dyslexia and also adults in FE. What disturbed me was that almost ALL dyslexics in the state system were never diagnosed. if they were it was too late, or when their parents coughed up £500 for a private psych's assessment.
Laying the blame at the Doon school who had Jack for 6 months (and no, they don't teach him for 24 hours a day so that comment is plain daft) is wrong.
You have no idea of dyslexia and how it's not possible to close a huge gap in 6 months. My bet is Jack's reading and comprehension ages were very low. English IGCSE is not a doddle; many non-dyslexics struggle to get a C.
Considering he was disengaged from lessons for so long at the Doon, they did well.