OP I have come across this thread late. I have skim read and only properly read your posts but I wanted to share my experience.
I have been teaching for 12 years in secondary school. When I first started we had proper study leave, they would leave somewhere around now and only come in for their exams. The problem for the school was as follows
a) some students didn't turn up for exams. In some subjects this was worse than others and counted against the subject on their overall results. if a student expects to fail or do very badly they may see it as not worth bothering with, also some just forget. Remember also the school is graded on how many 9-1 grades they achieve.
b) Students that might be between grades (this particularly matters when they are D/C 3/4 ) often dropped a grade compared with how they were doing in the lead up, suggesting that their revision method was poor or they weren't revising.
I have always been against this system for the majority because the truth is that apart from the worst areas and schools in the country most schools have a majority of students who revise. I would say somewhere around 60-80% would revise at home and we have changed the rules to cater for the minority. Also as you have said the higher ability miss out on an opportunity to revise what they need to revise and are forced to do the topic the teacher tells them to .As a student this would have been less effective for me and I think my grades would have been lower had this been the case when I was at school. I strongly believe this will prevent the hardworking students from revising well and will force them to revise additionally therefore believe this will create additional stress for the most hardworking.
Conversely I believe that those students the system is trying to help will actually convince themselves they have revised because they have been at school so they won't do any additional revision at the evenings and weekends. I have also found that some of the students the system is set up for don't work any harder than they would have at home. iIt's the hardworking ones who work hard!!!
I do acknowledge that there are some students who live in circumstances that mean they can't revise very easily at home and totally agree with making school available to them. It's making it compulsory that I don't agree with
A few years ago a big report (don't ask me to name it) suggested that students are leaving school less equipped to deal with situations in a functional and independent way. As teachers we were asked to try and find ways to develop more independent learners. Our response was to get rid of study leave!?! Anecdotally I have seen no improvement in grades or attitudes to learning.
If you want your daughter to revise at home my advice (I doubt it will be popular) would be to let her. I suppose in theory the school could fine you though.
I know this is a very long response but just wanted to add that this has nothing to do with class. Plenty of working class children are able and plenty of working class children are hardworking. There are also loads of working class families who support their children in their revision. It is often middle class families who expect the school to offer more and more revision and after school sessions etc.