I found this link when searching for The GHS website. It has been interesting to read people's perceptions of GHS, some accurate and some misleading. Both my sons have been to GHS , one academic and one not so. My youngest son is still there.
GHS has pupils who are in the top 5% of pupils in the UK academically and they are supported by the Gifted and Talented program. It is a small school granted, but staff turnover is low which brings many benefits for the children as the teachers know there strengths and weaknesses . Both my lads found/find it a very nurturing environment. Children develop emotionally and physically at different rates and in a small environment this difference can be magnified, but by and large the tutors and staff are supportive and most things get resolved. The plus side of this is that the groups can be very supportive of each other as they know each other well.
The GCSE options are standard and the children are supported to gain the best they can,with up to 9 GCSE's ( you only need 8 for entry) They also offer Latin for the more able children along with Spanish and French.
It is not a school for every child, but every school State and Independent has its own culture and atmosphere and does not suit everyone.
On the down side, communication about activities are sometimes vague as there is an expectation of assumed knowledge by the children and parents. This is improving though .
The school may not have the facilities of Kingswood or King Edwards, but it is developing and improving.
My eldest son joined the school from a State primary that was listed as one of the best in the region, it was not working for him and we saw his motivation crashing. He went to GHS, they quietly without fuss took him aside and built his confidence and English language skills , he gained a B in English and 9 GCSE's at A and B.
We looked at options for my youngest a son and decided that we want him to get a good grounding in English Maths and Science and a more traditional education, where he can actually enjoy learning, he can specialise or take more vocational subjects post 16.
He is an academic boy and yes probably would gain more GCSE's at King Edwards but we want him to enjoy learning at this stage.
I would suggest you visits on your own and then with your lad and see if it matches his needs and personality.