It's not clear to us if the OP's son is on a bursary and scholarship now, or just will be on a new scholarship from September when he moves to the college part of his school. It is certainly true that some schools and Heads are better than others with scholarships and bursaries, both in awarding them and how the recipients are then treated at school. It is definitely worth looking into the school's recent past and present record on these things. Information should be available in the press, online, the school's terms and conditions, and with the Charities Commission. I realise these things are often kept quiet for various reasons, some good and some not so good, but talk to other parents you can trust about what they know. A lot can be gained from sharing experience in confidence, including support. Certainly the school is remiss for not being clear with the OP in advance about the terms and conditions of her son's new scholarship. Do check on this Ragnar, and make sure you get it in writing and signed as a contract, because both sides need to be clear about what you are committing your son and yourself to and for how long, because you will be held to it and possibly more by the Head - or they might even try to renege on it. Scholarships are generally worth around a 10% reduction on full fees these days, in our experience.
Unfortunately at our school/college awards are not always made on merit, but by being favoured by the Head either by close friendship, total loyalty, or by donations or benefits in kind to the school or the Head. It sounds like the OP's son genuinely deserves his award however, so let's hope it all works out very well for him.
Generally, your son and you his parents will be required to take a full part in school/college life. This is especially so if the college is attached to a boarding school, where the culture includes evenings, weekends and trips away. Unless you fall into the favoured category, in our experience, 'scholarly behaviour ' will be expected at all times ie working very hard, making maximum effort, achieving excellent grades, making progress, looking smart and being ever polite, faultless conduct in behaviour, setting an excellent example to other children, caring for others, and generally being an excellent ambassador for the school/college and a credit to it. Not always easy for any child, let alone a young one or a teenage boy! If you are favoured, you can get away with an awful lot however!
On the subject of bursaries, many schools and Heads take a great pride in what they provide, including welcoming those pupils who genuinely do need and deserve maximum financial support. They also take a great interest and pride in what those pupils then go on to achieve, including in adult life. There is also an acknowledgement that ex-bursary pupils might well be able to help the school in the future in return. We couldn't recommend our school to such families, sadly. The Head has been open about wanting to spend the money on other things, and not wanting poor people at the school who do not fit in and can not afford all the extras we do. And yes, I am quoting him, unfortunately.