Reading the JCQ guidelines for GCSEs this year, it states that
Schools and colleges also have the option to set tests for you in order to gather further evidence. Teachers can develop these tests or use assessment materials provided by the exam boards. Importantly, these tests are not formal exams, nor are they designed to play the role of exams
What if a school only used formal exams in the exact form of GCSEs and marked in the exact same way a normal GCSE is with grade boundaries with the dcs teacher not having any say in what grade they think a dc is at? Subsequently the marks at this school are lower than other schools in the area despite it being a high performing selective school.