Why children don't go to school?

There's no school near where they live, they might be barred from attending school, because they are women, or belong to a minority religion, or skin color. They are forced to work to support the family. They have abusive parents. They ran away from home, and can not go to school, because they have to find a way to live. There country might be at war and it is too dangerous to go to school, such as Syria. Most children on the planet Earth can usually go to school, but, that is not always the case.