As a private teacher, I have many piano/organ/keyboard students taking GCSE music at their respective schools.
Based on the observations, complaints, anxieties of current pupils and those of previous years, they ALL say that the syllabus covers to much and that the teachers do not give enough explanation and background to the subjects.
I can give examples:
Listening Tests - Is this piece of music from the Baroque, Classical, Romantic or Modern period?
Quite often, the students tell me that they have had ONE listening lesson before being expected to answer this question. ONE example of each is given - no discussion on why, or how a piece is deemed to be Baroque, Classical, whatever, no discussion on the features of the compositions and the composers that worked within those periods, no comparison between different periods.
Recently a pupil came to me with a list of various vocal forms as given to the class. They had to find out and explain the difference between Opera, Operetta, Cantata, Oratorio, Chanson, etc.
A couple of weeks later, he told me that whilst he had completed the list, it had all been done via textbooks, although he had taken up my suggestion of raiding the music library and finding examples of each. However, at school, the lists were handed in, EVENTUALLY marked - subject closed!!!!!

No attempt on the teachers part to let the pupils HEAR examples of each, no input from the teacher at all.
The big problem is that some pupils opt for GCSE music without any knowledge of an instrument whatsoever - it's taken as "an easy option", and those pupils that DO have musical knowledge are often left to fend for themselves whilst teacher tries to bring the others up to a level.
What pupils find most disheartening is when they have produced a piece of coursework, composition, or whatever, and the teacher gives it scant regard. This is a specific source of anguish at two (un-named) local schools. I often end up assessing it for them to give them some idea of what level they have achieved, otherwise, once again, input from the teacher is neglible.
PLEASE do not take this as a slight against GCSE music teachers in general - these are some (and only some) of the experiences that I find common in this area.
I disturbs me that I hear the same comments from generation to generation of GCSE music students, and wonder whether the syllabus DOES cover far to much, and that each subject is only skated over.
Good luck