Some great advice above, it really depends on what your lad would enjoy more - I think most of us would way prefer more track time in a car you can really push but others just love the idea of at least having a go in a Ferrari / Lambo etc so they can say they've done it...
I think the best of all the track days you can do in this country has to be the Palmer sport days...
http://www.palmersport.co.uk/
I was lucky enough to do it through work and unfortunately it's not cheap but even 3 years later I still have great memories of it and would recommend anyone to do it if they can justify the money - It really is an experience of a life time....
The Instructors are mainly part time racing drivers and are all generally quite young - they even get competitive with the other instructors so don't stop pushing you all the way, even to the point where you're spinning a 911 at 90mph through a chicane, there's huge run-offs and loads of room on track that you really get to push all the cars to the limit (and beyond).
I really hope I can do it again one day!