This is a good question and my story is pretty dramatic. On my father's side, he came from a country that war devastated by war. For this reason, they lost pretty much their whole life. They barely escaped to another country. Eventually found their way to America. While my father was here in America, he worked hard and became an engineer. Through this he worked his way up to become a managing director of a company. You can say that he really achieved the American dream.
He sent his kids to college and graduate school. Now he is retired and has many grand children. From this perspective, there was a lot of social mobility. From having nothing and fleeing from a country to living in security and comfort.