Mimzan - it may be that way in Primary - I teach secondary, and the TAs were there for the specific students, and not all of them. If they hadn't spent the lesson dealing with that child, especially those that couldn't read or write, nothing would have been taught, as some of these students had EBDs as well, and spent time kicking off during lessons and disrupting others. By the time they get to secondary, there is no 'stigma' to having a TA specifically with you. It helps the students with their social skills and they have an adult to break down the task for them into chunks they can cope with. This is not possible for a teacher to do without a TA, and 30+ other students of mixed abilities in the class, as you have to get round them all.
The language issue is a problem for those who can't read/write English fluently if they are in secondary and in a GCSE class!
I guess also it depends on the demographic of where you are, as to the racial mix you get. I taught in rural Cornwall in a comp of 1400, with 1 mixed parentage lass, and a couple of Bulgarians. The racial mix just isn't there, although the social mix went from professional parents to those not in work.
The school my lad is in now goes from kindergarten to sixth form, about 1400 students in total, and 62 different nationalities, which is standard for Brussels, as NATO and the EU is here, and many companies have offices here as well. My son is experiencing more diversity here than he would had we stayed in the UK.
I chose to send him to prep in the UK, rather than the village school, as I wanted to avoid SATS and a prescribed curriculum. I also wanted him to do sport every afternoon and enjoy learning. I would either have tried to get him into grammar for secondary, or paid again for private schooling, as I don't like the National Curriculum - it doesn't allow time for delving into what is interesting and is supposed to be taught with an element of political correctness.
I would also have wanted him to do IGCSEs as they are more rigorous academically than the current GCSEs (I am a GCSE examiner and have just seen the new syllabus for my subject - all the difficult bits taken out), so I do feel able to comment.
The decision to go private for us not taken on 'class' grounds, but as a teacher with a child who I know would coast and get lost/avoid the teachers gaze in a large comp. Private education gives small class sizes and therefore more awareness as a teacher what is going on with your students. You can target them more effectively and raise their game. If the state system could achieve this, and more children in deprived areas were coming out of primaries able to read and write, then state education would improve. The bottom line for me however, is that while I have a choice, I will send my son to a school which achieves 80%+ A*-C at GCSE, rather than the 54% achieved by the state schools local to me were I in the UK.