I used to work on the railways. The company I worked for normally recruited their train conductors through external advertising. They were seeking people with a good general standard of education (because there's a surprising amount of safety training involved) and with 'people skills'.
Drivers, on the other hand, were generally recruited internally, with conductors and platform staff (who have the basic safety training already) opting to train to become drivers. One of the entry tests for driver training assessed how good candidates were at retaining concentration for long periods, with the more intelligent candidates often failing the test because there minds would wander too easily. (i.e.it helps if you're not too bright!)
There were also distinct personality characteristics that separated conductors and drivers. The vast majority of conductors were easy-going and likeable, whereas many drivers were irritable and arrogant, looking down their noses at other staff. It's often said on the railways that drivers think that they're God but they know that they can't be, because God sits in the signal box! (Signallers are the real 'bosses' on the railways, for valid safety reasons).
These links might also help:
Conductors:
https://nationalcareersservice.direct.gov.uk/advice/planning/jobprofiles/Pages/trainconductor.aspx
Drivers:
https://nationalcareersservice.direct.gov.uk/advice/planning/jobprofiles/Pages/traindriver.aspx
and, since one route to becoming a driver is to join the platform staff:
https://nationalcareersservice.direct.gov.uk/advice/planning/jobprofiles/Pages/trainstationstaff.aspx
Also, given that teenagers tend to change their minds quite often, you might like to have this link bookmarked for future reference:
https://nationalcareersservice.direct.gov.uk/advice/planning/jobfamily/Pages/default.aspx