Hi mumbytheriver, I hope I'm not too late but I'm a pupil at BC who's about to enter the Upper Sixth. I'm here to give some friendly advice about making what can be a very difficult decision to send your child to a school like BC. I realise that some of this stuff might have been said already but I do know a bit more about the application process etc.
Sixth at Brighton College is fantastic, especially if you have a child who is bright, willing to learn and willing to get stuck in elsewhere in College life. I joined the school after CE at 13+ so I haven't been through the entry into the Sixth Form myself but have many friends who have made the transition incredibly successfully.
Places are very competitive and are given on the basis of various factors, one of which is that your child will achieve their predicted GCSE grades. These will be the first thing the College asks for and should be high, with a good smattering of A*s in order to be able to compete not only with pupils already at the school but those who are joining from elsewhere into Sixth Form.
Another factor is pre-testing. Prospective students will be invited to attend an assessment day at the College where they will complete a series of Verbal Reasoning, English and Maths papers and a General paper assessing aptitudes in scientific reasoning, logic and writing.
Either on the same day or soon afterwards students will be interviewed by a senior member of one or two of the departments that your DS might join for his A-Level studies. Depending on which teacher you get will depend on how tough the interview is but as a general rule, your DS should be up to date on current affairs and developments in their chosen subjects as well as having a more specific area of interest within that subject.
Finally, the College will ask for a confidential reference from you DS's current school which should be provided along with his predicted GCSE grades.
New pupils at Sixth Form are expected to be some of the best academically in their year group with most applying to Oxbridge in their Upper Sixth year. However, if your DS finds the transition difficult, which can happen, the academic and pastoral support is second to none. Teachers at BC want every child to succeed and fulfill their potential and so will go out of their way to put on extra clinics and out of timetable lessons so that this can happen for your DS.
You mentioned that your son has ADHD. This will be taken into account throughout the application process and the school will do all they can to accommodate him. Once he is at the College he will recieve first class support from the lovely teachers at the SEN centre during his free periods.
I hope this is in some way useful to you. A final bit of advice to your DS would be to just relax and be himself during the assessments. Brighton College is a great school that suits all sorts of people and I'm sure your DS will love it here. I would recommend coming to one of our open days to find out more and see the College for yourselves. The next one is on 24th September for the whole College and on 15th October for Sixth Form entry specifically. If you have any more questions about College life please don't hesitate to ask. Alternatively you can contact our head of Sixth Form, Mr Patton, who would be happy to talk to you further about the application process.