Hmmm, we moved to this area purely because of the access to single sex grammar schools. DH and I were huge exponents of the grammar system, because DH excelled at his grammar and I was privately educated. Luckily, both our teens passed the 11+, ended up with amazing GCSEs and are both now in the sixth form.
So, on paper, being grammar schooled has really benefitted them academically but only on paper, literally their exam certificates. In reality, the grammar school was an Exam Factory and turned them into Superlative Exam Passing Machines.
As far as I can tell, there was very little learned about a love of learning, or encouraging an openly enquiring mind? Basically, if the knowledge wasn't of direct benefit to them, in a test or exam, my teens weren't that interested in knowing it. But, my God, they know the exam marking schemes back to front, and have had exam technique drilled into them on a daily basis. Their exam answers are pitch perfect, not a wasted word or calculation. They're robots. Exam robots.
Yet, despite their brilliant exam results, neither of our teens could reliably point to bloody Austria on a map! And, recently the younger teen (very likely to go to Oxbridge or LSE) asked me if Queen Victoria had any children! But, presumably this information was never necessary in a test or exam, so was irrelevant.
On a side note, I have just bought them the DK Childrens' Atlas and a fucking, illuminated globe for Xmas. And, we're going to have fucking lessons 