What are STATE schools in London like?

marytuda - are you talking about the wandsworth test? Of course it was full of prep school kids - all the local state primary kids had already taken the test in school

Yes, London state secondaries are now considered overall to be among the best in the country.

Why do people educate privately? Of course it is 90% snobbery. There is no other explanation. Maybe 10% of children (of the rich and priviliged) really wouldn't fare well in some of the more rufty tufty comprehensives. Shame for the kids who flounder there who don't have rich parents eh?

I've been following the exploding offers thread and thinking the same - why do London parents put themselves through that for the privilege of paying out however many thousands a year it is now for the next 7 years?
I think you have some of the answers OP - family habits and snobbery . . Racism also in the mix I fear; London state schools are, like inner London itself, surprise surprise, virtually all majority minority-ethnic . . . . Many indeed 100% minority-ethnic (though usually far from mono-ethnic, unlike (so I've heard) in a place like Bradford.)
That means they have no white kids at all! Imagine that, if you are from a posh or poshish all-white background yourself (bar the servants . . .) My poor little darlings!!
I've also gathered (from exploding offers thread) that the only type of state school any private school applicant would conceivably consider is a grammar school - apparently it's only the grammar results they are hanging on for as their private offers explode.
As parent of Y6 child I am also awaiting state school offers day with keen interest, but not desperation: all our 6 chosen inner London comprehensives are impressive in different ways, and my uncomplicated, able DS will be fine I am fairly sure at any of them.
What they are really like I'm not yet in a position to report first hand, obviously, but I am optimistic; the teaching, the kids, even the facilities many have access to (sometimes borrowing from the privates) are impressive - as are the academic results achieved Without Selection at 11!
In London - newsflash! - you really don't have to pay out a small fortune Or subject your 10 year old to a battery of 11+ examinations to access a top class education! Most parents desperate to do so are in my view either so moneyed the cash is of no consequence, or deluded. Or both.
The only thing that worries me a bit is state funding cuts, meaning it may be necessary to supplement extra-curricular stuff a bit more than a private school parent would.
I am, just about, from a generation where all state school kids in the country were pretty much forced to pass or fail (mostly fail) the 11 +. It was frankly cruel, even for those of us who passed, for reasons I won't elaborate now. I naively thought all that went out in the 1970s (except in Theresa May's constituency, and Kent, so I hear) so was sorry to find my 10 year old facing it again for privilege of applying for Any (including non-selective) state school in one of our neighbouring (Traditionally Tory) London boroughs.

Unprepared as he was, it was the only one of a series of "special aptitude" assessments I put him through (a means for even state comps to select a bit on the side, another story) that he minded. "Don't ever make me do another one like that, Mum," he said afterwards. I absolutely promised not to.
Incidentally, that 11+ day was full of prep school kids, some of whose parents are probably now agitating about exploding offers as they wait to see if their DC has got into, um, Graveney it would be. You could tell, partly, by how white everyone there was in comparison to our usual cohort.

Exactly as you say in your last sentence, @tenentimestwo.
The schools are fine. Classes are large, money is short and extracurricular activities are limited compared to what would be on offer at a school like CLSG, but the actual teaching is probably pretty similar. The biggest hurdle to a bright kid in a big-standard comp (in my experience) is poor behaviour / time wasting from other students and lower expectations (they’re already in the top 50% of achievers if they listen in class and actually bother to do, and hand in their homework).
If they can overcome that and still get top grades, those top grades are worth far more than those belonging to someone coming from a top few-paying school. Clearly not everyone can.
My DC’s mixed comp in inner London is Ofsted outstanding but extremely socially mixed with a very high proportions of free school meals and English as a second language, with many students coming from some of the most deprived areas of London. The long and short of it is that by paying, you are removing your child from these “obstacles” to learning and planting them in a like minded social circle.
Most of my friends and family have chosen a different route to me, but I see the well-rounded people my DCs are becoming, accepting of everyone, and have no regrets at my choice.