Does anyone have any experience with working at, attended yourself, or have/had kids a PK/K-12 school?

I'm curious with what it's like to be in this environment with kids of all ages and grades in the same building. Do these schools usually exist in smaller towns? How are the younger children protected and kept safe? Are some cles grade combined (for example 1st and 2nd grade?) Are kids separated by grades in different parts of the building? What grade does a child get to play a sport and participate in social activities like dances? What grade does the one teacher for every subject stop? What about recess? How does each grade get adequate time to use the library and gym? I can't see how this type of school benefits kids. Different levels of schools (elem, middle, high) have different needs for kids emotionally and academically and I can't see how one school can meet all of those needs.