This is a good initiative.
I work as a casual worker at a shitty establishment with a number of young people, for many of whom this is their first job. Recently I became the place's first union delegate, and heard from a number of people that they'd asked the managers about joining a union, and were uniformly told that there was no applicable union to become a member of (in one case, someone was told that joining a union was in the agreement as a sackable offence).
While undoubtedly it takes a great amount of naivete for these workers to believe these utter lies from management, it also shows that people so easily misled are most in need of having union protection. Given there's no programme in the school system regarding this, it is good for the unions to go out and get this themselves. Seeing, at my school, guest speakers from business groups came in to speak in business studies classes and our careers advisory class, it stands to reason that union reps should be given an opportunity to explain the role of unions in careers and in business.
Of course the Murdoch press has a problem with this, and the same conservative apparatchiks here whinge, but clearly people need to be educated on the subject, and until it's put into the school curriculum (and even then, should a unionist with some insight into the system not be allowed to give a guest lecture regarding it, if called upon) how else should the message be got out?