2 people in my year repeated, their ATARs did improve, but not significantly
whereas a number of people in my year (with ATARs in 70s/80s) did general degrees e.g. B Arts, B Science got C/D/HD average and transferred into law, engineering, commerce etc. at USYD/UNSW
for chemistry, learn to titrate with precision the slightest mistake can cost you a lot of marks, also learn to make the perfect graph with line of best fit and correct x,y labels
always use a simple one line conclusion that relates to your aim
also be wary of the resources they give you in...
850 - 1100 is pretty decent
thread reminds me of my dodgy english teacher who praised me for writing the most number of pages ... "everyone you have to fill all the lines in the booklets given if you want band 6" :/