Uni must have changed then. When I went through there was heaps of support services available, as well as tutorials on top of the lectures. If you feel like you are on your own, then I don't think you may have been looking hard enough.
Uni is still like this the support is there but unlike school YOU have to seek it out. In high school a good teacher will see a struggling student and help them but inUni if you did not understand the content YOU had to make an appointment with the lecturer or Tutorial aid.
The other thing you need at uni is self disipline because dont turn up to a lecture no one will care dont hand in an assingment no one will chase you up you just get a big F and have to do the course again too many F's and then someone will chase you up and have a hard discussion about is this the place for you
If you have a child with self displine problems i cannot reccomend highly enough TAFE as a gateway to uni. You will get Uni credits for the course you do and it is a cross between high school and Uni so you get eased into that "support is only there if you go looking for it model"
I can speak from experience i failed my HSC with a TER of 42% went to TAFE for 1.5 years and studied businees passed in the credit grade. Went to uni continued business with OHS got a years worth of credist for for my TAFE corse only had to do 2 years and walked out with a degree in the credit grade so i was only 6 months behind my mates that went straght to uni and half of them had to do an extra semester anyway
Since then have worked as a National Safety Manager for 2 of Oz largest compaines, National OHS project manager for a 3rd and Compliance Coord for Australias Largest Oil and Gas construction project and have been invited back to TAFE to lecure as a Subject matter expert in between
So yeah at the end of the day whils the HSC is important it is more the behaviour and disipline at uni that will make or break a student. It is not the end of the world if they dont do well in the HSC cause it is amazing the marks that go up when they are picking subjects of interest to them