Too many students think that Year 11 is not very important - that it is just the year between the end of the School Certificate and the beginning of the Higher School Certificate in Term 4. This is not the case. It is in the first three terms of Year 11 that the foundations for your Year 12 exams are set. Not for nothing is it called the Preliminary Higher School Certificate. For some courses, how you perform in Year 11 decides which level of courses you can continue into Year 12, particularly in relation to Extension Courses and Maths levels.
From the beginning of Year 11 to the end of your schooling in Year 12 is 7 terms or, approximately, 70 weeks of classes. Take out of that, 6 weeks of exams, and that leaves just 64 weeks (approximately) for you to complete these subjects. Now that may sound a lot but it is not really, particularly if you take out occasional excursions, incursions, sports carnivals and study days.
This is an unfortunate name to give those class times when you do not have formal classes because, when you first find that you have them, you think WOW! Time Off!
Instead you should be thinking WOW! An opportunity to do some private study!
This is, of course, very hard to face when you would much rather relax, socialise and do it legally at school.
You must try to find a balance. On some occasions by all means socialise, but, in the majority of cases make use of your time to do the sort of private study you may not be able to do at home such as consulting reference books in the library, or tidying up notes just taken in a class while it is still fresh in your mind.
Above all don't "waste" the time. It can never be regained.