@OneSwallowSummer
I've always thought the next tier down from the top even for a very bright child is a better choice. The pace and pressure is relentless at the top and there's no room to falter. You need solid pastoral care and great teaching without behaviour problems. It's not rocket science. The preoccupation with secondary schools is uniquely British. In most of the world where you go to secondary isn't ever a topic of conversation.
I’m not sure which countries you are thinking about but where I’m coming from, people very much worry about which secondary schools children are going to. And they go to great length to be sure their dcs go to the ‘right’ school, just like in the U.K.
The reason is simple. Not all schools are actually equal.
As @OneSwallowSummer said
You need solid pastoral care and great teaching without behaviour problems.
The problem is, a school like that isn’t always easy to find…. At least, it’s not where I live.