This is really difficult. I was a Head of Drama and so am used to advising students on these matters. My single most important piece of advice would be that students really should appply for courses that are very, very well respected. The industry is of course highly competetive and so if your DS wants to do a course to help him on his way then it should be a well regarded one otherwise he may as well throw his hat in the ring without any course at all.
Doing a BA course from a well respected university in Drama and Theatre Studies would mean that your DS is in a good position to set up his own pieces of work because he is likely to have the opportunity to develop skills in technical elements of theatre as well, as well as develop academically. He could invite agents to them and tour around so that when it comes to searching for acting jobs he is not merely waiting impotently by the phone. (These courses require high A Level grades. Usually AAA or ABB.)
They say you have to be single minded about this and not plan for other eventualities. Some people advise against having 'something to fall back on' but if your 'something to fall back on' can help you whilst you're waiting for that 'phone call' then it will make living life and having success in performance easier to come by.
In terms of help for drama school auditions it could be worth contacting a local LAMDA or Guildhall Speech and Drama teacher who could really help with audition pieces.
Be careful which audition pieces you choose. My usual advice would be to choose ones that you don't think other people will do so that you stand out. On the other hand, doing something too strange could make it difficult for the people holding the auditions to see how you could be cast both on the course and in the industry.
Drama schools seem to look for 'types', much as that may seem unsavoury, it seems to be how these things work. Most people are 'type cast' these days so it is worth thinking about what 'type' you might be and working with, rather than against this.
It's late so I'm sorry if this has come out in a rather chaotic sort of a way but I was keen to get some ideas down quickly for you!
Break a leg!