How much did you guys study over the summer hols :O?
I was at work for most of the holidays, so I'm probably not the best person to askAs Stick said, Year 12 is a marathon, not a sprint - Good way to put it! I got through all of my Holidays Homework, but I didn't do a lot of extra study. Don't do the whole textbook for all your subjects, but may be do a chapter of 2 extra ahead of your class.
Everyone is different, and sometimes I get distracted as well in class, like Stick. But in Year 12, your teachers are gonna teach you the content, but they are gonna expect you to do the rest. You need to manage time very wisely - One of the key elements to surviving Year 12. If you fall behind, you've got a long road to catch up. So if you do have Time management issues, then do a FEW extra chapters over the holidays, but please don't do the whole book for each Subject! I've seen this mentioned a few times on AN.
So yeah, you need to work at the pace you feel comfortable with. Because Year 12 is all about you - Its whatever you want to achieve out of it. You get what you put in - But it doesn't mean you go ahead of your school by a lot of chapters, otherwise you will also forget content (Particularly for science subjects), but not so much for Maths subjects.