Just that really, honestly?
I've got a child starting school in 2019. Older sibling went through our local school and has now left. Doing fine in KS3.
Dc1 had a few problems at the school, nothing too serious, low level stuff like getting easily distracted, chatting in class. All pretty much ironed out by the time they left, never got in serious trouble or anything like that.
On the whole dc1 has a happy time at the school, but at times lots of things could have gone better. Things dc could have done better, things I could have done better and things that the school could have done better.
I'm looking at sending dc2 to the school however I don't want them to be prejudged based on their older sibling. I want them to have every chance in their own right as an individual.
They're very different children so I'd hope they'd be treated as such.