Agreed, the "socialising" is where I hear "hanging out with my mates" and as you say, most do that.
For school leavers we don't ask competency questions and we have any GCSE or A Level grades from the application point, so from their point of view there's usually not much to highlight where/what they've learnt. I find with apprentices what really works for us is making sure they'll fit in. We hire those who show a keen interest in whatever the apprenticeship is in (I hire for admin, accounting, HR and occasionally IT), those with an outside passion for something, regardless of what it is, someone with a bit of confidence, personable and smiley, and where you can tell they've prepared for the interview. That means well dressed (I'm not expecting suit and tie but office wear or neat and tidy is expected) and a couple of thoughtful answers.
Questions I tend to ask school leavers (with no, or very little work experience):
What makes you interested in a career in finance/HR/IT/admin?
What do you do outside of school/hobbies?
What are your medium or long term goals? Can be either personal or professional. I'm not expecting them to have prepared anything for this but it's nice to hear when candidates want to progress eventually onto a level 7 qualification, or (such as previously mentioned) the person training for a half marathon said they'd eventually like to run the London marathon.
Favourite subject in school and why? The answer isn't important but again, it often sparks a conversation about what they're passionate about.
I also love it when they've got a question at the end for me, it shows they've prepared for the interview.