Most of the answers have been preachy and way off topic. Those who answered with useful info - thank you very much for taking the time.
If you have no experience of consultants then don't post. I did not come here for lectures on all the above.
I'm a UK academic at a top ranked university in the Humanities, so can't speak with more than generalist collegial knowledge of STEM. I've also taught Humanities in the US and other countries, so I'm aware of the more broad-ranging curriculum in the 4 year US degree.
I suggest that instead of being snippy you mine this MN forum for all the experience & knowledge that exists here. Most posters have DC going through university in the UK, or like me, teach at UK universities. There is a wealth of knowledge.
The UCAS website is also very searchable, so put in the variables of what your DS wants, and see what it throws up.
Consultants are not a thing in the UK. The better/richer schools do a good job in trying to match pupils with likely institutions. The rest sink or swim, but use this forum, and The Student Room, to help.
It would help if you could tell us roughly the area of his general ambitions for a degree. There is so much knowledge in this forum from parents & academics, you should use it, instead of being snippy.
Also, where does he think he'd like to live post graduation? And what might he want to do? I would always advise that if a UK student wants to study in the US but work & live ultimately in the UK, they should g to the best university their grades & interview permit in the UK, and which offers the opportunity for a year abroad at a highly-ranked US school ( eg. we send ours to UT (Austin) which has the top ranked department in my discipline).
My advice for your DS is similar but vice versa. If he thinks he wants to return to work in the US, pick the best US school his grades & essays & extra-curriculars allow, and one which offers a year abroad. DD of a US friend was at a v good NYC school (Barnard) which offered a year in Oxford, for example.
The 4 year broad-based US degree is very like an Australian degree, and both are based on the Scottish system, so that might be a place to focus.
Believe me, consultants are a US thing. And if you're paying for a prep like Groton or Andover, I'm surprised they can't guide you. I've done consulting work in Hong Kong, where there's a huge & mobile international community & the schools there are very active in getting good international information for their pupils (why I was there, actually).
It is a very different system, but for UK citizens, rather less daunting than the US applications as applicants have only 5 choices, via UCAS. Pupils here in the UK (as you might remember) only study 3 subjects at A Level, and that is much closer to a freshman year in the US. Have you thought of him doing his Freshman year in the US, to get his bearings, and then applying for UK courses? I find when I teach US exchange/year abroad students, they come to us as Juniors, but we place them in our second year courses - they're about a year behind generally - but they all end up pretty much even.
I think you may have to do some research of your own - for free! - to have ready suggestions for him. It's great you've already been to some of the universities so he has a feel for where he would spend 3 years away from his familiar support network. And you must be proud of him that he's "Harvard material" but that won't necessarily get him a place at a top UK university ... it's a different process. We're not particularly interested in all the "citizenship" and "leadership" stuff. It's the ability & potential for critical thinking we're looking for.