Interestingly the data shows that 11+ results have very little bearing on GCSE results. There's no direct correlation between a high 11+ score and top GCSE grades. DCs at grammar schools tend to do better at GCSE for a whole host of reasons, but those reasons do not include 'doing well at the 11+'. Perhaps that's because, as various PPs have said, the 11+ isn't curriculum based and is limited and specific in what it tests?
Just picking up on a couple of points raised, the notion that grammar schools aid social mobility just is not true, in Bucks, at least. They do the exact opposite. I think this might have been the original, and laudable, aim, but it is not how they function these days.
The socio-economic mix of any grammar MUST match that of its catchment. So while the school can select, it must select the most able from each group rather than simply taking the most able overall.
This is an intriguing idea @LouisCatorze has it ever been attempted? Or even suggested (except by you of course!)
It’s an unfair system because there are many kids who are late bloomers, many kids who are very good at academic subjects not measured by the test, work ethic is very important to eventual success.
This sums up my stance perfectly @BungleandGeorge. There are also DCs who might have had caring responsibilities, who might have experienced tragedy and trauma, who might have had a chaotic early home life, who might be struggling with illness or injury, who might be very good at 1 or 2 subjects and hopeless at others, who might not be very good at tests but thrive in group work or course work. And so on. All in all just too many variables for anyone to be making irrevocable decisions at 10, we need more flexibility in the system than that.