>We must have left some poor but capable kids in the wrong school.
Both of those things cannot be true at the same time. Either school is important, in which case both the parents pushing their children and the children pushing themselves are doing the right thing to improve their chances of later success, or it is NOT important, in which case it doesn't matter anyway which school the other children end up in.
Trying to get a less academic kid into grammar school isn't going to help them. Maybe I can provide a bit of context.
The grammar school is highly academic. The kid is certainly above my level of attainment when I was his age. I went to a non-selective international school, ending with the IB.
The kids are tested, every week, in a variety of subjects. I don't think a week has gone by without some sort of test. It is a constant grind of math, multiple sciences, humanities, and three languages. Not every kid enjoys that kind of thing, or even benefits from the pressure.
If you manage to Fosbury Flop your kid into a school like this, you're actually doing them a disservice. They will hate being constantly pushed academically, and they will not find fellowship with the kind of kid who enjoys it.
At the same time, there will be poor kids who didn't know the tricks of the exam, and didn't get in, who would have been better off at the school.
Some children can be pushed way too hard, some can be pushed not enough and certainly some parents can take their own personal ambitions way too far, as it sounds like in the case you are describing.
Unfortunately, at the end of the day, I don't know of any system anywhere in the world that hasn't eventually devolved into a status chase, for better or worse.
Argument #1: Certain kids are privileged enough to be able to afford tutoring and get into good schools and this is unfair to the poor kids
Argument #2: Certain kids are being pushed UNNECESSARILY by their parents to participate in a rat race when their time would be better suited to doing something else
If certain kids are getting in because of tutoring rather than because of talent/ability, then they are the kids that are being pushed unnecessarily to participate when they'd be better off doing something else. Those kids take up the space of kids who are poor who could benefit from that kind of instruction.
Especially since the kid who was in "the wrong school" will be blamed for "being lazy" or "less capable" when they don't perform as well as equally capable and hardworking peers in the "right school".
Kids in real world selective schools do form relationships, are curious, interact and like the world outside. Some selective schools are like you describe ... but others are not and kids in them are happy.
There's a difference between considering something important versus an utmost priority. The parent's criticism refers to the latter, which is also typical in certain cultures (here, in the context of USA).
I've had direct experience with middle-class schools and indirect experience with an upper-class one, and the issues with the latter are very tangible. The most horrific cases involve parents of students who are not capable enough (in the given context) and will do everything in the book to ensure their children succeed, at the expense of both the children themselves and the whole system. Then, of course, if one considers study/career the one and only priority, emotional and relational needs are seen as a hindrance, creating successful but emotionally damaged adults.
Ultimately, this can be summarized with the Mexican fisherman story, I guess (which omits that the businessman is a cocaine addict, cheats on his wife, and has never spent time with his children /s).