The attitude seems to be "Elbows out girls and get to the top, however much you have to stand on other people's fingers along the way".
There is a lot of testing and repeat testing if a mid-term score is less X%.
Judgement of your daughter' s progress will be by how many "Excellent" grades she gets, not by whether or not she is happy.
I am a GHS parent (Y9) and interestingly this is the opposite of my experience. My daughter feels supported by her teachers and peers, only last week she told me that 'we're not competitive, we're kind and help each other.' I've never heard of repeat testing.
Admittedly my daughter is bright and making good progress. Most importantly, she is very happy at the school, has some lovely friends, is making the most of the opportunities available and feels "accepted for who she is."
DD2 is even brighter (IQ>140) & has an offer to join in September, but we are considering other options because we're not sure she'd love it in the same way. It's certainly not for everyone, but an excellent school for the right child.