Since you'd technically be considered an adult, the only way they could forcibly take you back is if they could prove to a court that you're unable to care for yourself due to a mental or physical condition.
But, just because they can't call the cops on you anymore, doesn't mean running away is a good idea.
For starters, what will it achieve? If you're worried about your grades or perhaps your parent's reaction - I can assure you that the fallout of not knowing where you are and whether you're safe or not will be far worse.
Secondly, if the prospect of getting poor results on an exam is stressing you out this much, how much of a breeze do you expect it to be when you have to fend for yourself, earn money, find a new place to stay etc... Once you've run away?
Finally, and I know this is going to sound like a bit of a cliché, but bad things will continue happening in your life from now until the day you die - that doesn't mean you need to take such drastic action.
Doing well in exams is important. It can help you get into the right college - which influence the rest of your life.
But the thing I've learned from my 28 years on this planet is that things run their course one way or another. Often, the thing that you least expected to happen can have a really positive outcome.
For example, I thought I was pretty happy with my life. Then I found out it was all going to change when we discovered were having a baby.
At first, the prospect of having to move city, leave all my friends behind and say goodbye to my lifestyle was pretty daunting.
In fact it's so scary that a lot of fathers just can't cope with it and leave.
But now not only do I have a lovely daughter - but I've made a whole set of brand new friends, I've got a job I really enjoy (that I never imagined I'd get before), and I've learned lots of new things.
Life still isn't perfect, but it never is - you've just gotta roll with the flow and pick up the bonus coins along the way - no point getting hung up on life's evil turtles and other obstacles...
