Where should you position the heaviest gear in the backpack

Depends on what you're worried about:
Yourself
Agility/Movement Speed
The Lighter Stuff In your pack

Really, the general rule: Pack the heaviest items at the bottom, keep what you're more likely to need at the top. Though always be prepared to NOT have your backpack and still be ok for a little, so it's best to make sure you have some extra stuff that is important in any pockets you have, preferably not the back pockets. 

But for your backpack, just keep the heavy stuff at the bottom, so not to crush any lighter objects, and keep the most important objects you are more likely to need sooner at the top. 

It depends on the subject for me. some exams are easier than others so i usually go through it and answer questions i know based on my general knowledge, then double check after. going through the lesson can a lot  because the exams can be  very lesson-specific, but sometimes they are ridiculously long so a lot of people don't take the time. i did find that, when i went through the lessons, i was making 100's on my exams vs strictly using + the internet and  i make 90's. 

For the sat there is a reading test, math test, and a writing and language test. the act has social studies and science tests.