Without wishing to rain on anyone's parade, very few high achieving schools are composed of mainly like minded girls in y7 8 9...unless in a superselective with minimal catchment considerations like one locally. There, girls have been working so hard to gain entry in part due to parental pressure.
In most highly academic schools locally, one sees the full gamut of behaviour including snidery towards the highest achievers; glorification of sporty types; daft, attention seeking & oblivious behaviour typical of teens in all schools.
I haven't really seen one of these schools which have a high minded positive regard for academics amongst my daughters' friends schools locally incl WHS PHS SHS LEH SWPS GHS KCS SPS SPGS CLGS & Hampton. All are filled with competitive kids. Views come from a few of the teachers too, who generally think that academics come into fashion amongst their students as the reality of GCSES bite.
Apologies if Oxford High School is different. But I truly doubt that any high school is much different (unless a boarding school starting in y9 where different atmospheres can prevail)
So - go in with eyes wide open!
(I have 3 at 3 different schools mentioned above and despite what I have said, would not change it. )