I know that they need to be overseen but they must be doing some
useful work during that period

But from the employer's point of view you need to subtract from the
value of the work they do the cost of telling/supervising/checking up on
them - especially the cost of the time of their "masters". Given the
latter are likely to cost an awful lot more per hour than the NMW
employers would be far less likely to take on apprentices if they had to
pay them the NMW when they are under 19 or in their first year. Of
course that may well be too difficult for the NUS to understand. Or of
course they might just say that employers should be compelled to take on
apprentices.

Do they also get paid for the tim whilst at college, I really don't
know
Yes they are (well, should by law) be paid.

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Robin
reply to address is (meant to be) valid