Reading Mum wrote:
super selective does not mean no catchment. In Kent there are super selectives which only take something like the top 3% of applicants, as opposed to Busks which offers places to about 30%.
You might get a better answer with a different title
It sort of does that, though - that there is no other barrier to entry Like comparing KEGS and CCHS in Chelmsford with CRGS and ColCHS in Colchester. The Chelmsford grammar schools reserve the first 80% of places for IC applicants. If the 120th IC girl applying for CCHS (PAN 150 IIRC) scored, say, 106 and the 31st OOC applicant scored, say 112, the 120th IC girl would get a place and the 31st OOC girl wouldn't, even though she was higher up in the overall rankings. Whereas the Colchester grammar schools have no catchment, ranking applicants only by score. So if the aforementioned two girls had also taken the CSSE exam and the OOC one ranked within PAN and the IC one didn't, the OOC girl would get a place and the IC girl wouldn't.
So there you go, OP, ColchesteIr County High School for Girls. Sitting the same exam, your DD can also compete for dedicated OOC places at Westcliff or Southend High School for Girls. Either way, you can move to the seaside if she gets in, which has got.to be an advantage over HBS

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But scary mum is quite right. Using the 'search' function should bring you many discussions on the subject.