Do your grandparents have legal custody or guardianship over you? If so, they would need to give permission for you to move out. Being 18 will happen soon enough and then they will have no obligation to support you, although many parents and grandparents continue to provide housing and financial assistance. While it may be that they don't understand you, you will have many years where you will have to take care of yourself. Don't be in too big a hurry.
I agree with David Littman that the answer depends on whether your grandparents have custody of you or not. If they don't, you could return to your parent or parents' home. If they do have custody of you then they are obligated to provide you with a place to live. They might call the police and report you as a missing child. Whether the police would force you to return to their home is an unknown considering your age. Police departments and their policies vary from county to county and officers themselves vary. I encourage you to continue to go to school regardless of what you do.