@stubiff it is the sheer volume of information they have to retain that is hard to comprehend unless your child has gone through it. DCs sat around 24 exams.
For English lit alone they had to know important themes, the order events took place, characters and quotes for 15 poems (plus form, structure, imagery) a Shakespeare play, a 20th century novel and a 19th century novel. That is one subject.
For History 5 topics and about 24 mini topics within each topic, dates, names of people, events, diseases. Each paper had different style questions and marks for answers. Some had sources provided some you had to know everything so more difficult as everything relies on knowledge and recall.
The earlier they start the easier it is because at this point they are still learning year 11 content to add to the year 10 stuff they should be able to recall. GCSEs are two part, one is understanding the content in the first place and secondly being able to recall or apply that knowledge.
Even a mock at this point will be one paper for English lit as they will probably be still working their way through a book. It depends on what grades they want, mine spent some of year 10 holidays working on what they lacked on the year 10 exam papers. Mine got similar results to user149. Mine are at a state school, they know that they are competing against students whose parents paid £25k a year for their children's education. The bell curve is always applied, you just have to try to do better than others.
Some revision is set as homework anyway but in all honesty when you work out how much free time teenagers have it can be the same amount of time they are in school, mine were out at 3pm, home by 3.25 and went to bed at 11pm. That is a lot of free time. No I didn't expect them to be doing homework at 10pm but they can come home and spend a few hours doing work before dinner. After all, lots of schools have homework clubs and fee paying schools have a longer school day.