We live in a grammar school area. Around here, tutoring is very common, I don't know of any child who didn't do plenty of preparation for the test. Ridiculous really, because all these children were already bright, most had graduate parents or from homes where education was highly valued etc. Just madness, but you get sucked into the system, you don't want your child to be the only non tutored one.
Both our DDs were tutored, though their tutor said on day one that he 'couldn't teach IQ' and all he could do was teach them good technique and a few tricks of the trade. I very much doubt our DDs needed the tutoring (or any of their friends) but I suppose it did mean they walked into the test very confidently.
Having said all that, plenty of children who were tutored still didn't pass? So tutoring isn't the magic wand that some people assume it to be.
Both our DDs have been through the grammar school system, but I'm not especially enamoured of it anymore. I won't deny that pupils attain excellent results, but they're essentially just Exam Factories. Teachers aren't really interested in explaining more than once, pupils are just expected to keep up. Pupils aren't taught to love learning, they're drilled in how to pass exams, and they do it extremely well.
It's a dry, relentless, unforgiving way to learn. But it garners results if what you're after is just a slew of great GCSEs and A Levels.