With the end of August comes the end of summer and the promises of a new school year. For some students, this brings the promise of a fresh start, but for those whose time in high school is coming to an end, it brings a whole new set of challenges, emotions and stress. National Geographic's new four-part documentary series American High School goes inside the senior year of students from Orangeburg, South Carolina, who share the highs and lows of their academic, athletic and…